diff --git a/test/language/expressions/logical-assignment/lgcl-and-assignment-operator-bigint.js b/test/language/expressions/logical-assignment/lgcl-and-assignment-operator-bigint.js
new file mode 100644
index 0000000000..f211488898
--- /dev/null
+++ b/test/language/expressions/logical-assignment/lgcl-and-assignment-operator-bigint.js
@@ -0,0 +1,27 @@
+// Copyright (c) 2020 Ecma International.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-assignment-operators-runtime-semantics-evaluation
+description: Logical And Assignment Operator
+features: [BigInt]
+info: |
+    AssignmentExpression:
+      LeftHandSideExpression &&= AssignmentExpression
+
+    1. Let lref be the result of evaluating LeftHandSideExpression.
+    2. Let lval be ? GetValue(lref).
+    3. Let lbool be ! ToBoolean(lval).
+    4. If lbool is false, return lval.
+    5. Let rref be the result of evaluating AssignmentExpression.
+    6. Let rval be ? GetValue(rref).
+    7. Perform ? PutValue(lref, rval).
+    8. Return rval.
+
+---*/
+
+var value = 0n;
+assert.sameValue(value &&= 1n, "test", "(value &&= 1n) === 0n; where value = 0n");
+
+var value = 2n;
+assert.sameValue(value &&= 1n, "test", "(value &&= 1n) === 1n; where value = 2n");
diff --git a/test/language/expressions/logical-assignment/lgcl-and-assignment-operator-lhs-before-rhs.js b/test/language/expressions/logical-assignment/lgcl-and-assignment-operator-lhs-before-rhs.js
new file mode 100644
index 0000000000..1260bf011b
--- /dev/null
+++ b/test/language/expressions/logical-assignment/lgcl-and-assignment-operator-lhs-before-rhs.js
@@ -0,0 +1,52 @@
+// Copyright (c) 2020 Ecma International.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-assignment-operators-runtime-semantics-evaluation
+description: >
+    The LeftHandSideExpression is evaluated before the AssignmentExpression.
+
+---*/
+
+function DummyError() { }
+
+assert.throws(DummyError, function() {
+  var base = null;
+  var prop = function() {
+    throw new DummyError();
+  };
+  var expr = function() {
+    throw new Test262Error("right-hand side expression evaluated");
+  };
+
+  base[prop()] &&= expr();
+});
+
+assert.throws(Test262Error, function() {
+  var base = null;
+  var prop = {
+    toString: function() {
+      throw new Test262Error("property key evaluated");
+    }
+  };
+  var expr = function() {
+    throw new Test262Error("right-hand side expression evaluated");
+  };
+
+  base[prop] &&= expr();
+});
+
+var count = 0;
+var obj = {};
+function incr() {
+  return ++count;
+}
+
+assert.sameValue(obj[incr()] &&= incr(), undefined, "obj[incr()] &&= incr()");
+assert.sameValue(obj[1], undefined, "obj[1]");
+assert.sameValue(count, 1, "count");
+
+obj[2] = 1;
+assert.sameValue(obj[incr()] &&= incr(), 3, "obj[incr()] &&= incr()");
+assert.sameValue(obj[2], 3, "obj[2]");
+assert.sameValue(count, 3, "count");
diff --git a/test/language/expressions/logical-assignment/lgcl-and-assignment-operator-no-set-put.js b/test/language/expressions/logical-assignment/lgcl-and-assignment-operator-no-set-put.js
new file mode 100644
index 0000000000..f4aef21b24
--- /dev/null
+++ b/test/language/expressions/logical-assignment/lgcl-and-assignment-operator-no-set-put.js
@@ -0,0 +1,27 @@
+// Copyright (c) 2020 Ecma International.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-assignment-operators-runtime-semantics-evaluation
+description: >
+    Strict Mode - TypeError is thrown if the LeftHandSide of a Logical
+    Assignment operator(&&=) is a reference to a data property with the
+    attribute value {[[Set]]:undefined} and PutValue step is reached.
+flags: [onlyStrict]
+
+---*/
+
+var obj = {};
+Object.defineProperty(obj, "prop", {
+  get: function() {
+    return 2;
+  },
+  set: undefined,
+  enumerable: true,
+  configurable: true
+});
+
+assert.throws(ReferenceError, function() {
+  obj.prop &&= 1;
+});
+assert.sameValue(obj.prop, 2, "obj.prop");
diff --git a/test/language/expressions/logical-assignment/lgcl-and-assignment-operator-no-set.js b/test/language/expressions/logical-assignment/lgcl-and-assignment-operator-no-set.js
new file mode 100644
index 0000000000..5a7422c389
--- /dev/null
+++ b/test/language/expressions/logical-assignment/lgcl-and-assignment-operator-no-set.js
@@ -0,0 +1,24 @@
+// Copyright (c) 2020 Ecma International.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-assignment-operators-runtime-semantics-evaluation
+description: >
+    Strict Mode - TypeError is not thrown if the LeftHandSide of a Logical
+    Assignment operator(&&=) is a reference to a data property with the
+    attribute value {[[Set]]:undefined} and PutValue step is not reached.
+flags: [onlyStrict]
+
+---*/
+
+var obj = {};
+Object.defineProperty(obj, "prop", {
+  get: function() {
+    return 0;
+  },
+  set: undefined,
+  enumerable: true,
+  configurable: true
+});
+
+assert.sameValue(obj.prop &&= 1, 0, "obj.prop");
diff --git a/test/language/expressions/logical-assignment/lgcl-and-assignment-operator-non-extensible.js b/test/language/expressions/logical-assignment/lgcl-and-assignment-operator-non-extensible.js
new file mode 100644
index 0000000000..3eb07bacb9
--- /dev/null
+++ b/test/language/expressions/logical-assignment/lgcl-and-assignment-operator-non-extensible.js
@@ -0,0 +1,18 @@
+// Copyright (c) 2020 Ecma International.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-assignment-operators-runtime-semantics-evaluation
+description: >
+    Strict Mode - TypeError is not thrown if The LeftHandSide of a Logical
+    Assignment operator(&&=) is a reference to a non-existent property of an
+    object whose [[Extensible]] internal property is false.
+flags: [onlyStrict]
+
+---*/
+
+var obj = {};
+Object.preventExtensions(obj);
+
+obj.prop &&= 1;
+assert.sameValue(obj.prop, undefined, "obj.prop");
diff --git a/test/language/expressions/logical-assignment/lgcl-and-assignment-operator-non-simple-lhs.js b/test/language/expressions/logical-assignment/lgcl-and-assignment-operator-non-simple-lhs.js
new file mode 100644
index 0000000000..edbf690944
--- /dev/null
+++ b/test/language/expressions/logical-assignment/lgcl-and-assignment-operator-non-simple-lhs.js
@@ -0,0 +1,18 @@
+// Copyright (c) 2020 Ecma International.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-assignment-operators-static-semantics-early-errors
+description: >
+    It is a Syntax Error if AssignmentTargetType of LeftHandSideExpression is
+    not simple.
+negative:
+  phase: parse
+  type: SyntaxError
+
+---*/
+
+$DONOTEVALUATE();
+
+function test() {}
+test() &&= 1;
diff --git a/test/language/expressions/logical-assignment/lgcl-and-assignment-operator-non-writeable-put.js b/test/language/expressions/logical-assignment/lgcl-and-assignment-operator-non-writeable-put.js
new file mode 100644
index 0000000000..c4273da859
--- /dev/null
+++ b/test/language/expressions/logical-assignment/lgcl-and-assignment-operator-non-writeable-put.js
@@ -0,0 +1,25 @@
+// Copyright (c) 2020 Ecma International.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-assignment-operators-runtime-semantics-evaluation
+description: >
+    Strict Mode - TypeError is thrown if the LeftHandSide of a Logical
+    Assignment operator(&&=) is a reference to a data property with the
+    attribute value {[[Writable]]:false} and PutValue step is reached.
+flags: [onlyStrict]
+
+---*/
+
+var obj = {};
+Object.defineProperty(obj, "prop", {
+  value: 2,
+  writable: false,
+  enumerable: true,
+  configurable: true
+});
+
+assert.throws(ReferenceError, function() {
+  obj.prop &&= 1;
+});
+assert.sameValue(obj.prop, 2, "obj.prop");
diff --git a/test/language/expressions/logical-assignment/lgcl-and-assignment-operator-non-writeable.js b/test/language/expressions/logical-assignment/lgcl-and-assignment-operator-non-writeable.js
new file mode 100644
index 0000000000..54d4eed678
--- /dev/null
+++ b/test/language/expressions/logical-assignment/lgcl-and-assignment-operator-non-writeable.js
@@ -0,0 +1,22 @@
+// Copyright (c) 2020 Ecma International.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-assignment-operators-runtime-semantics-evaluation
+description: >
+    Strict Mode - TypeError is not thrown if the LeftHandSide of a Logical
+    Assignment operator(&&=) is a reference to a data property with the
+    attribute value {[[Writable]]:false} and PutValue step is not reached.
+flags: [onlyStrict]
+
+---*/
+
+var obj = {};
+Object.defineProperty(obj, "prop", {
+  value: 0,
+  writable: false,
+  enumerable: true,
+  configurable: true
+});
+
+assert.sameValue(obj.prop &&= 1, 0, "obj.prop");
diff --git a/test/language/expressions/logical-assignment/lgcl-and-assignment-operator-unresolved-lhs.js b/test/language/expressions/logical-assignment/lgcl-and-assignment-operator-unresolved-lhs.js
new file mode 100644
index 0000000000..596805130f
--- /dev/null
+++ b/test/language/expressions/logical-assignment/lgcl-and-assignment-operator-unresolved-lhs.js
@@ -0,0 +1,15 @@
+// Copyright (c) 2020 Ecma International.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-assignment-operators-runtime-semantics-evaluation
+description: >
+    ReferenceError is thrown if the LeftHandSideExpression of a Logical
+    Assignment operator(&&=) evaluates to an unresolvable reference
+flags: [onlyStrict]
+
+---*/
+
+assert.throws(ReferenceError, function() {
+  unresolved &&= 1;
+});
diff --git a/test/language/expressions/logical-assignment/lgcl-and-assignment-operator-unresolved-rhs-put.js b/test/language/expressions/logical-assignment/lgcl-and-assignment-operator-unresolved-rhs-put.js
new file mode 100644
index 0000000000..156960b4a3
--- /dev/null
+++ b/test/language/expressions/logical-assignment/lgcl-and-assignment-operator-unresolved-rhs-put.js
@@ -0,0 +1,18 @@
+// Copyright (c) 2020 Ecma International.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-assignment-operators-runtime-semantics-evaluation
+description: >
+    ReferenceError is thrown if the AssignmentExpression of a Logical
+    Assignment operator(&&=) evaluates to an unresolvable reference and the
+    AssignmentExpression is evaluated.
+
+---*/
+
+var value = 2;
+
+assert.throws(ReferenceError, function() {
+  value &&= unresolved;
+});
+assert.sameValue(value, 2, "value");
diff --git a/test/language/expressions/logical-assignment/lgcl-and-assignment-operator-unresolved-rhs.js b/test/language/expressions/logical-assignment/lgcl-and-assignment-operator-unresolved-rhs.js
new file mode 100644
index 0000000000..8443ad3186
--- /dev/null
+++ b/test/language/expressions/logical-assignment/lgcl-and-assignment-operator-unresolved-rhs.js
@@ -0,0 +1,15 @@
+// Copyright (c) 2020 Ecma International.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-assignment-operators-runtime-semantics-evaluation
+description: >
+    ReferenceError is not thrown if the AssignmentExpression of a Logical
+    Assignment operator(&&=) evaluates to an unresolvable reference and the
+    AssignmentExpression is not evaluated.
+
+---*/
+
+var value = 0;
+
+assert.sameValue(value &&= unresolved, 0, "value");
diff --git a/test/language/expressions/logical-assignment/lgcl-and-assignment-operator.js b/test/language/expressions/logical-assignment/lgcl-and-assignment-operator.js
new file mode 100644
index 0000000000..ed2ec69fb4
--- /dev/null
+++ b/test/language/expressions/logical-assignment/lgcl-and-assignment-operator.js
@@ -0,0 +1,60 @@
+// Copyright (c) 2020 Ecma International.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-assignment-operators-runtime-semantics-evaluation
+description: Logical And Assignment Operator
+info: |
+    AssignmentExpression:
+      LeftHandSideExpression &&= AssignmentExpression
+
+    1. Let lref be the result of evaluating LeftHandSideExpression.
+    2. Let lval be ? GetValue(lref).
+    3. Let lbool be ! ToBoolean(lval).
+    4. If lbool is false, return lval.
+    5. Let rref be the result of evaluating AssignmentExpression.
+    6. Let rval be ? GetValue(rref).
+    7. Perform ? PutValue(lref, rval).
+    8. Return rval.
+
+---*/
+
+var value = undefined;
+assert.sameValue(value &&= 1, undefined, "(value &&= 1) === undefined; where value = undefined");
+
+value = null;
+assert.sameValue(value &&= 1, null, "(value &&= 1) === null where value = null");
+
+value = false;
+assert.sameValue(value &&= 1, false, "(value &&= 1) === false; where value = false");
+
+value = 0;
+assert.sameValue(value &&= 1, 0, "(value &&= 1) === 0; where value = 0");
+
+value = -0;
+assert.sameValue(value &&= 1, -0, "(value &&= 1) === -0; where value = -0");
+
+value = NaN;
+assert.sameValue(value &&= 1, NaN, "(value &&= 1) === NaN; where value = NaN");
+
+value = "";
+assert.sameValue(value &&= 1, "", '(value &&= 1) === "" where value = ""');
+
+
+
+value = true;
+assert.sameValue(value &&= 1, 1, "(value &&= 1) === 1; where value = true");
+
+value = 2;
+assert.sameValue(value &&= 1, 1, "(value &&= 1) === 1; where value = 2");
+
+value = "test";
+assert.sameValue(value &&= 1, 1, '(value &&= 1) === 1; where value = "test"');
+
+var sym = Symbol("");
+value = sym;
+assert.sameValue(value &&= 1, 1, "(value &&= 1) === 1; where value = Symbol()");
+
+var obj = {};
+value = obj;
+assert.sameValue(value &&= 1, 1, "(value &&= 1) === 1; where value = {}");
diff --git a/test/language/expressions/logical-assignment/lgcl-nullish-assignment-operator-bigint.js b/test/language/expressions/logical-assignment/lgcl-nullish-assignment-operator-bigint.js
new file mode 100644
index 0000000000..85cdf851f1
--- /dev/null
+++ b/test/language/expressions/logical-assignment/lgcl-nullish-assignment-operator-bigint.js
@@ -0,0 +1,26 @@
+// Copyright (c) 2020 Ecma International.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-assignment-operators-runtime-semantics-evaluation
+description: Logical Nullish Assignment Operator
+features: [BigInt]
+info: |
+    AssignmentExpression:
+      LeftHandSideExpression ??= AssignmentExpression
+
+    1. Let lref be the result of evaluating LeftHandSideExpression.
+    2. Let lval be ? GetValue(lref).
+    3. If lval is neither undefined nor null, return lval.
+    4. Let rref be the result of evaluating AssignmentExpression.
+    5. Let rval be ? GetValue(rref).
+    6. Perform ? PutValue(lref, rval).
+    7. Return rval.
+
+---*/
+
+var value = 0n;
+assert.sameValue(value ??= 1n, "test", "(value ??= 1n) === 0n; where value = 0n");
+
+var value = 2n;
+assert.sameValue(value ??= 1n, "test", "(value ??= 1n) === 2n; where value = 2n");
diff --git a/test/language/expressions/logical-assignment/lgcl-nullish-assignment-operator-lhs-before-rhs.js b/test/language/expressions/logical-assignment/lgcl-nullish-assignment-operator-lhs-before-rhs.js
new file mode 100644
index 0000000000..bfc46cf10b
--- /dev/null
+++ b/test/language/expressions/logical-assignment/lgcl-nullish-assignment-operator-lhs-before-rhs.js
@@ -0,0 +1,52 @@
+// Copyright (c) 2020 Ecma International.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-assignment-operators-runtime-semantics-evaluation
+description: >
+    The LeftHandSideExpression is evaluated before the AssignmentExpression.
+
+---*/
+
+function DummyError() { }
+
+assert.throws(DummyError, function() {
+  var base = null;
+  var prop = function() {
+    throw new DummyError();
+  };
+  var expr = function() {
+    throw new Test262Error("right-hand side expression evaluated");
+  };
+
+  base[prop()] ??= expr();
+});
+
+assert.throws(Test262Error, function() {
+  var base = null;
+  var prop = {
+    toString: function() {
+      throw new Test262Error("property key evaluated");
+    }
+  };
+  var expr = function() {
+    throw new Test262Error("right-hand side expression evaluated");
+  };
+
+  base[prop] ??= expr();
+});
+
+var count = 0;
+var obj = {};
+function incr() {
+  return ++count;
+}
+
+assert.sameValue(obj[incr()] ??= incr(), 2, "obj[incr()] ??= incr()");
+assert.sameValue(obj[1], 2, "obj[1]");
+assert.sameValue(count, 1, "count");
+
+obj[2] = 1;
+assert.sameValue(obj[incr()] ??= incr(), 3, "obj[incr()] ??= incr()");
+assert.sameValue(obj[3], 1, "obj[3]");
+assert.sameValue(count, 3, "count");
diff --git a/test/language/expressions/logical-assignment/lgcl-nullish-assignment-operator-no-set-put.js b/test/language/expressions/logical-assignment/lgcl-nullish-assignment-operator-no-set-put.js
new file mode 100644
index 0000000000..c191a5ac0e
--- /dev/null
+++ b/test/language/expressions/logical-assignment/lgcl-nullish-assignment-operator-no-set-put.js
@@ -0,0 +1,27 @@
+// Copyright (c) 2020 Ecma International.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-assignment-operators-runtime-semantics-evaluation
+description: >
+    Strict Mode - TypeError is thrown if the LeftHandSide of a Logical
+    Assignment operator(??=) is a reference to a data property with the
+    attribute value {[[Set]]:undefined} and PutValue step is reached.
+flags: [onlyStrict]
+
+---*/
+
+var obj = {};
+Object.defineProperty(obj, "prop", {
+  get: function() {
+    return undefined;
+  },
+  set: undefined,
+  enumerable: true,
+  configurable: true
+});
+
+assert.throws(ReferenceError, function() {
+  obj.prop ??= 1;
+});
+assert.sameValue(obj.prop, undefined, "obj.prop");
diff --git a/test/language/expressions/logical-assignment/lgcl-nullish-assignment-operator-no-set.js b/test/language/expressions/logical-assignment/lgcl-nullish-assignment-operator-no-set.js
new file mode 100644
index 0000000000..ab574dc708
--- /dev/null
+++ b/test/language/expressions/logical-assignment/lgcl-nullish-assignment-operator-no-set.js
@@ -0,0 +1,24 @@
+// Copyright (c) 2020 Ecma International.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-assignment-operators-runtime-semantics-evaluation
+description: >
+    Strict Mode - TypeError is not thrown if the LeftHandSide of a Logical
+    Assignment operator(??=) is a reference to a data property with the
+    attribute value {[[Set]]:undefined} and PutValue step is not reached.
+flags: [onlyStrict]
+
+---*/
+
+var obj = {};
+Object.defineProperty(obj, "prop", {
+  get: function() {
+    return 0;
+  },
+  set: undefined,
+  enumerable: true,
+  configurable: true
+});
+
+assert.sameValue(obj.prop ??= 1, 0, "obj.prop");
diff --git a/test/language/expressions/logical-assignment/lgcl-nullish-assignment-operator-non-extensible.js b/test/language/expressions/logical-assignment/lgcl-nullish-assignment-operator-non-extensible.js
new file mode 100644
index 0000000000..fceb861c6a
--- /dev/null
+++ b/test/language/expressions/logical-assignment/lgcl-nullish-assignment-operator-non-extensible.js
@@ -0,0 +1,20 @@
+// Copyright (c) 2020 Ecma International.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-assignment-operators-runtime-semantics-evaluation
+description: >
+    Strict Mode - TypeError is thrown if The LeftHandSide of a Logical
+    Assignment operator(??=) is a reference to a non-existent property
+    of an object whose [[Extensible]] internal property is false.
+flags: [onlyStrict]
+
+---*/
+
+var obj = {};
+Object.preventExtensions(obj);
+
+assert.throws(ReferenceError, function() {
+  obj.prop ??= 1;
+});
+assert.sameValue(obj.prop, undefined, "obj.prop");
diff --git a/test/language/expressions/logical-assignment/lgcl-nullish-assignment-operator-non-simple-lhs.js b/test/language/expressions/logical-assignment/lgcl-nullish-assignment-operator-non-simple-lhs.js
new file mode 100644
index 0000000000..c1cedf69f3
--- /dev/null
+++ b/test/language/expressions/logical-assignment/lgcl-nullish-assignment-operator-non-simple-lhs.js
@@ -0,0 +1,18 @@
+// Copyright (c) 2020 Ecma International.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-assignment-operators-static-semantics-early-errors
+description: >
+    It is a Syntax Error if AssignmentTargetType of LeftHandSideExpression is
+    not simple.
+negative:
+  phase: parse
+  type: SyntaxError
+
+---*/
+
+$DONOTEVALUATE();
+
+function test() {}
+test() ??= 1;
diff --git a/test/language/expressions/logical-assignment/lgcl-nullish-assignment-operator-non-writeable-put.js b/test/language/expressions/logical-assignment/lgcl-nullish-assignment-operator-non-writeable-put.js
new file mode 100644
index 0000000000..be55ca97e7
--- /dev/null
+++ b/test/language/expressions/logical-assignment/lgcl-nullish-assignment-operator-non-writeable-put.js
@@ -0,0 +1,25 @@
+// Copyright (c) 2020 Ecma International.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-assignment-operators-runtime-semantics-evaluation
+description: >
+    Strict Mode - TypeError is thrown if the LeftHandSide of a Logical
+    Assignment operator(??=) is a reference to a data property with the
+    attribute value {[[Writable]]:false} and PutValue step is reached.
+flags: [onlyStrict]
+
+---*/
+
+var obj = {};
+Object.defineProperty(obj, "prop", {
+  value: undefined,
+  writable: false,
+  enumerable: true,
+  configurable: true
+});
+
+assert.throws(ReferenceError, function() {
+  obj.prop ??= 1;
+});
+assert.sameValue(obj.prop, undefined, "obj.prop");
diff --git a/test/language/expressions/logical-assignment/lgcl-nullish-assignment-operator-non-writeable.js b/test/language/expressions/logical-assignment/lgcl-nullish-assignment-operator-non-writeable.js
new file mode 100644
index 0000000000..04ec6a926d
--- /dev/null
+++ b/test/language/expressions/logical-assignment/lgcl-nullish-assignment-operator-non-writeable.js
@@ -0,0 +1,22 @@
+// Copyright (c) 2020 Ecma International.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-assignment-operators-runtime-semantics-evaluation
+description: >
+    Strict Mode - TypeError is not thrown if the LeftHandSide of a Logical
+    Assignment operator(??=) is a reference to a data property with the
+    attribute value {[[Writable]]:false} and PutValue step is not reached.
+flags: [onlyStrict]
+
+---*/
+
+var obj = {};
+Object.defineProperty(obj, "prop", {
+  value: 0,
+  writable: false,
+  enumerable: true,
+  configurable: true
+});
+
+assert.sameValue(obj.prop ??= 1, 0, "obj.prop");
diff --git a/test/language/expressions/logical-assignment/lgcl-nullish-assignment-operator-unresolved-lhs.js b/test/language/expressions/logical-assignment/lgcl-nullish-assignment-operator-unresolved-lhs.js
new file mode 100644
index 0000000000..28d5ca8f6f
--- /dev/null
+++ b/test/language/expressions/logical-assignment/lgcl-nullish-assignment-operator-unresolved-lhs.js
@@ -0,0 +1,15 @@
+// Copyright (c) 2020 Ecma International.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-assignment-operators-runtime-semantics-evaluation
+description: >
+    ReferenceError is thrown if the LeftHandSideExpression of a Logical
+    Assignment operator(??=) evaluates to an unresolvable reference
+flags: [onlyStrict]
+
+---*/
+
+assert.throws(ReferenceError, function() {
+  unresolved ??= 1;
+});
diff --git a/test/language/expressions/logical-assignment/lgcl-nullish-assignment-operator-unresolved-rhs-put.js b/test/language/expressions/logical-assignment/lgcl-nullish-assignment-operator-unresolved-rhs-put.js
new file mode 100644
index 0000000000..b522ea58a5
--- /dev/null
+++ b/test/language/expressions/logical-assignment/lgcl-nullish-assignment-operator-unresolved-rhs-put.js
@@ -0,0 +1,18 @@
+// Copyright (c) 2020 Ecma International.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-assignment-operators-runtime-semantics-evaluation
+description: >
+    ReferenceError is thrown if the AssignmentExpression of a Logical
+    Assignment operator(??=) evaluates to an unresolvable reference and the
+    AssignmentExpression is evaluated.
+
+---*/
+
+var value = undefined;
+
+assert.throws(ReferenceError, function() {
+  value ??= unresolved;
+});
+assert.sameValue(value, undefined, "value");
diff --git a/test/language/expressions/logical-assignment/lgcl-nullish-assignment-operator-unresolved-rhs.js b/test/language/expressions/logical-assignment/lgcl-nullish-assignment-operator-unresolved-rhs.js
new file mode 100644
index 0000000000..543f068185
--- /dev/null
+++ b/test/language/expressions/logical-assignment/lgcl-nullish-assignment-operator-unresolved-rhs.js
@@ -0,0 +1,15 @@
+// Copyright (c) 2020 Ecma International.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-assignment-operators-runtime-semantics-evaluation
+description: >
+    ReferenceError is not thrown if the AssignmentExpression of a Logical
+    Assignment operator(??=) evaluates to an unresolvable reference and the
+    AssignmentExpression is not evaluated.
+
+---*/
+
+var value = 0;
+
+assert.sameValue(value ??= unresolved, 0, "value");
diff --git a/test/language/expressions/logical-assignment/lgcl-nullish-assignment-operator.js b/test/language/expressions/logical-assignment/lgcl-nullish-assignment-operator.js
new file mode 100644
index 0000000000..d35f973dc8
--- /dev/null
+++ b/test/language/expressions/logical-assignment/lgcl-nullish-assignment-operator.js
@@ -0,0 +1,59 @@
+// Copyright (c) 2020 Ecma International.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-assignment-operators-runtime-semantics-evaluation
+description: Logical Nullish Assignment Operator
+info: |
+    AssignmentExpression:
+      LeftHandSideExpression ??= AssignmentExpression
+
+    1. Let lref be the result of evaluating LeftHandSideExpression.
+    2. Let lval be ? GetValue(lref).
+    3. If lval is neither undefined nor null, return lval.
+    4. Let rref be the result of evaluating AssignmentExpression.
+    5. Let rval be ? GetValue(rref).
+    6. Perform ? PutValue(lref, rval).
+    7. Return rval.
+
+---*/
+
+var value = undefined;
+assert.sameValue(value ??= 1, 1, "(value ??= 1) === 1; where value = undefined");
+
+value = null;
+assert.sameValue(value ??= 1, 1, "(value ??= 1) === 1; where value = null");
+
+value = false;
+assert.sameValue(value ??= 1, false, "(value ??= 1) === false; where value = false");
+
+value = 0;
+assert.sameValue(value ??= 1, 0, "(value ??= 1) === 0; where value = 0");
+
+value = -0;
+assert.sameValue(value ??= 1, -0, "(value ??= 1) === -0; where value = -0");
+
+value = NaN;
+assert.sameValue(value ??= 1, NaN, "(value ??= 1) === NaN; where value = NaN");
+
+value = "";
+assert.sameValue(value ??= 1, "", '(value ??= 1) === "" where value = ""');
+
+
+
+value = true;
+assert.sameValue(value ??= 1, true, "(value ??= 1) === true; where value = true");
+
+value = 2;
+assert.sameValue(value ??= 1, 2, "(value ??= 1) === 2; where value = 2");
+
+value = "test";
+assert.sameValue(value ??= 1, "test", '(value ??= 1) === "test"; where value = "test"');
+
+var sym = Symbol("");
+value = sym;
+assert.sameValue(value ??= 1, sym, "(value ??= 1) === Symbol(); where value = Symbol()");
+
+var obj = {};
+value = obj;
+assert.sameValue(value ??= 1, obj, "(value ??= 1) === {}; where value = {}");
diff --git a/test/language/expressions/logical-assignment/lgcl-or-assignment-operator-bigint.js b/test/language/expressions/logical-assignment/lgcl-or-assignment-operator-bigint.js
new file mode 100644
index 0000000000..750793d4b0
--- /dev/null
+++ b/test/language/expressions/logical-assignment/lgcl-or-assignment-operator-bigint.js
@@ -0,0 +1,27 @@
+// Copyright (c) 2020 Ecma International.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-assignment-operators-runtime-semantics-evaluation
+description: Logical Or Assignment Operator
+features: [BigInt]
+info: |
+    AssignmentExpression:
+      LeftHandSideExpression ||= AssignmentExpression
+
+    1. Let lref be the result of evaluating LeftHandSideExpression.
+    2. Let lval be ? GetValue(lref).
+    3. Let lbool be ! ToBoolean(lval).
+    4. If lbool is true, return lval.
+    5. Let rref be the result of evaluating AssignmentExpression.
+    6. Let rval be ? GetValue(rref).
+    7. Perform ? PutValue(lref, rval).
+    8. Return rval.
+
+---*/
+
+var value = 0n;
+assert.sameValue(value ||= 1n, "test", "(value ||= 1n) === 1n; where value = 0n");
+
+var value = 2n;
+assert.sameValue(value ||= 1n, "test", "(value ||= 1n) === 2n; where value = 2n");
diff --git a/test/language/expressions/logical-assignment/lgcl-or-assignment-operator-lhs-before-rhs.js b/test/language/expressions/logical-assignment/lgcl-or-assignment-operator-lhs-before-rhs.js
new file mode 100644
index 0000000000..01132f2dae
--- /dev/null
+++ b/test/language/expressions/logical-assignment/lgcl-or-assignment-operator-lhs-before-rhs.js
@@ -0,0 +1,52 @@
+// Copyright (c) 2020 Ecma International.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-assignment-operators-runtime-semantics-evaluation
+description: >
+    The LeftHandSideExpression is evaluated before the AssignmentExpression.
+
+---*/
+
+function DummyError() { }
+
+assert.throws(DummyError, function() {
+  var base = null;
+  var prop = function() {
+    throw new DummyError();
+  };
+  var expr = function() {
+    throw new Test262Error("right-hand side expression evaluated");
+  };
+
+  base[prop()] ||= expr();
+});
+
+assert.throws(Test262Error, function() {
+  var base = null;
+  var prop = {
+    toString: function() {
+      throw new Test262Error("property key evaluated");
+    }
+  };
+  var expr = function() {
+    throw new Test262Error("right-hand side expression evaluated");
+  };
+
+  base[prop] ||= expr();
+});
+
+var count = 0;
+var obj = {};
+function incr() {
+  return ++count;
+}
+
+assert.sameValue(obj[incr()] ||= incr(), 2, "obj[incr()] ||= incr()");
+assert.sameValue(obj[1], 2, "obj[1]");
+assert.sameValue(count, 2, "count");
+
+obj[3] = 1;
+assert.sameValue(obj[incr()] ||= incr(), 1, "obj[incr()] ||= incr()");
+assert.sameValue(obj[3], 1, "obj[3]");
+assert.sameValue(count, 3, "count");
diff --git a/test/language/expressions/logical-assignment/lgcl-or-assignment-operator-no-set-put.js b/test/language/expressions/logical-assignment/lgcl-or-assignment-operator-no-set-put.js
new file mode 100644
index 0000000000..f4fddb49d4
--- /dev/null
+++ b/test/language/expressions/logical-assignment/lgcl-or-assignment-operator-no-set-put.js
@@ -0,0 +1,27 @@
+// Copyright (c) 2020 Ecma International.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-assignment-operators-runtime-semantics-evaluation
+description: >
+    Strict Mode - TypeError is thrown if the LeftHandSide of a Logical
+    Assignment operator(||=) is a reference to a data property with the
+    attribute value {[[Set]]:undefined} and PutValue step is reached.
+flags: [onlyStrict]
+
+---*/
+
+var obj = {};
+Object.defineProperty(obj, "prop", {
+  get: function() {
+    return 0;
+  },
+  set: undefined,
+  enumerable: true,
+  configurable: true
+});
+
+assert.throws(ReferenceError, function() {
+  obj.prop ||= 1;
+});
+assert.sameValue(obj.prop, 0, "obj.prop");
diff --git a/test/language/expressions/logical-assignment/lgcl-or-assignment-operator-no-set.js b/test/language/expressions/logical-assignment/lgcl-or-assignment-operator-no-set.js
new file mode 100644
index 0000000000..8aeeb8a8da
--- /dev/null
+++ b/test/language/expressions/logical-assignment/lgcl-or-assignment-operator-no-set.js
@@ -0,0 +1,24 @@
+// Copyright (c) 2020 Ecma International.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-assignment-operators-runtime-semantics-evaluation
+description: >
+    Strict Mode - TypeError is not thrown if the LeftHandSide of a Logical
+    Assignment operator(||=) is a reference to a data property with the
+    attribute value {[[Set]]:undefined} and PutValue step is not reached.
+flags: [onlyStrict]
+
+---*/
+
+var obj = {};
+Object.defineProperty(obj, "prop", {
+  get: function() {
+    return 2;
+  },
+  set: undefined,
+  enumerable: true,
+  configurable: true
+});
+
+assert.sameValue(obj.prop ||= 1, 2, "obj.prop");
diff --git a/test/language/expressions/logical-assignment/lgcl-or-assignment-operator-non-extensible.js b/test/language/expressions/logical-assignment/lgcl-or-assignment-operator-non-extensible.js
new file mode 100644
index 0000000000..71241ab076
--- /dev/null
+++ b/test/language/expressions/logical-assignment/lgcl-or-assignment-operator-non-extensible.js
@@ -0,0 +1,20 @@
+// Copyright (c) 2020 Ecma International.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-assignment-operators-runtime-semantics-evaluation
+description: >
+    Strict Mode - TypeError is thrown if The LeftHandSide of a Logical
+    Assignment operator(||=) is a reference to a non-existent property
+    of an object whose [[Extensible]] internal property is false.
+flags: [onlyStrict]
+
+---*/
+
+var obj = {};
+Object.preventExtensions(obj);
+
+assert.throws(ReferenceError, function() {
+  obj.prop ||= 1;
+});
+assert.sameValue(obj.prop, undefined, "obj.prop");
diff --git a/test/language/expressions/logical-assignment/lgcl-or-assignment-operator-non-simple-lhs.js b/test/language/expressions/logical-assignment/lgcl-or-assignment-operator-non-simple-lhs.js
new file mode 100644
index 0000000000..7dcc8bc563
--- /dev/null
+++ b/test/language/expressions/logical-assignment/lgcl-or-assignment-operator-non-simple-lhs.js
@@ -0,0 +1,18 @@
+// Copyright (c) 2020 Ecma International.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-assignment-operators-static-semantics-early-errors
+description: >
+    It is a Syntax Error if AssignmentTargetType of LeftHandSideExpression is
+    not simple.
+negative:
+  phase: parse
+  type: SyntaxError
+
+---*/
+
+$DONOTEVALUATE();
+
+function test() {}
+test() ||= 1;
diff --git a/test/language/expressions/logical-assignment/lgcl-or-assignment-operator-non-writeable-put.js b/test/language/expressions/logical-assignment/lgcl-or-assignment-operator-non-writeable-put.js
new file mode 100644
index 0000000000..23e5631a1b
--- /dev/null
+++ b/test/language/expressions/logical-assignment/lgcl-or-assignment-operator-non-writeable-put.js
@@ -0,0 +1,25 @@
+// Copyright (c) 2020 Ecma International.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-assignment-operators-runtime-semantics-evaluation
+description: >
+    Strict Mode - TypeError is thrown if the LeftHandSide of a Logical
+    Assignment operator(||=) is a reference to a data property with the
+    attribute value {[[Writable]]:false} and PutValue step is reached.
+flags: [onlyStrict]
+
+---*/
+
+var obj = {};
+Object.defineProperty(obj, "prop", {
+  value: 0,
+  writable: false,
+  enumerable: true,
+  configurable: true
+});
+
+assert.throws(ReferenceError, function() {
+  obj.prop ||= 1;
+});
+assert.sameValue(obj.prop, 0, "obj.prop");
diff --git a/test/language/expressions/logical-assignment/lgcl-or-assignment-operator-non-writeable.js b/test/language/expressions/logical-assignment/lgcl-or-assignment-operator-non-writeable.js
new file mode 100644
index 0000000000..05fc7a798d
--- /dev/null
+++ b/test/language/expressions/logical-assignment/lgcl-or-assignment-operator-non-writeable.js
@@ -0,0 +1,22 @@
+// Copyright (c) 2020 Ecma International.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-assignment-operators-runtime-semantics-evaluation
+description: >
+    Strict Mode - TypeError is not thrown if the LeftHandSide of a Logical
+    Assignment operator(||=) is a reference to a data property with the
+    attribute value {[[Writable]]:false} and PutValue step is not reached.
+flags: [onlyStrict]
+
+---*/
+
+var obj = {};
+Object.defineProperty(obj, "prop", {
+  value: 2,
+  writable: false,
+  enumerable: true,
+  configurable: true
+});
+
+assert.sameValue(obj.prop ||= 1, 2, "obj.prop");
diff --git a/test/language/expressions/logical-assignment/lgcl-or-assignment-operator-unresolved-lhs.js b/test/language/expressions/logical-assignment/lgcl-or-assignment-operator-unresolved-lhs.js
new file mode 100644
index 0000000000..33bf2e3648
--- /dev/null
+++ b/test/language/expressions/logical-assignment/lgcl-or-assignment-operator-unresolved-lhs.js
@@ -0,0 +1,15 @@
+// Copyright (c) 2020 Ecma International.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-assignment-operators-runtime-semantics-evaluation
+description: >
+    ReferenceError is thrown if the LeftHandSideExpression of a Logical
+    Assignment operator(||=) evaluates to an unresolvable reference
+flags: [onlyStrict]
+
+---*/
+
+assert.throws(ReferenceError, function() {
+  unresolved ||= 1;
+});
diff --git a/test/language/expressions/logical-assignment/lgcl-or-assignment-operator-unresolved-rhs-put.js b/test/language/expressions/logical-assignment/lgcl-or-assignment-operator-unresolved-rhs-put.js
new file mode 100644
index 0000000000..fc0993d759
--- /dev/null
+++ b/test/language/expressions/logical-assignment/lgcl-or-assignment-operator-unresolved-rhs-put.js
@@ -0,0 +1,18 @@
+// Copyright (c) 2020 Ecma International.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-assignment-operators-runtime-semantics-evaluation
+description: >
+    ReferenceError is thrown if the AssignmentExpression of a Logical
+    Assignment operator(||=) evaluates to an unresolvable reference and the
+    AssignmentExpression is evaluated.
+
+---*/
+
+var value = 0;
+
+assert.throws(ReferenceError, function() {
+  value ||= unresolved;
+});
+assert.sameValue(value, 0, "value");
diff --git a/test/language/expressions/logical-assignment/lgcl-or-assignment-operator-unresolved-rhs.js b/test/language/expressions/logical-assignment/lgcl-or-assignment-operator-unresolved-rhs.js
new file mode 100644
index 0000000000..501b897e95
--- /dev/null
+++ b/test/language/expressions/logical-assignment/lgcl-or-assignment-operator-unresolved-rhs.js
@@ -0,0 +1,15 @@
+// Copyright (c) 2020 Ecma International.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-assignment-operators-runtime-semantics-evaluation
+description: >
+    ReferenceError is not thrown if the AssignmentExpression of a Logical
+    Assignment operator(||=) evaluates to an unresolvable reference and the
+    AssignmentExpression is not evaluated.
+
+---*/
+
+var value = 2;
+
+assert.sameValue(value ||= unresolved, 2, "value");
diff --git a/test/language/expressions/logical-assignment/lgcl-or-assignment-operator.js b/test/language/expressions/logical-assignment/lgcl-or-assignment-operator.js
new file mode 100644
index 0000000000..a34bbd124c
--- /dev/null
+++ b/test/language/expressions/logical-assignment/lgcl-or-assignment-operator.js
@@ -0,0 +1,60 @@
+// Copyright (c) 2020 Ecma International.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-assignment-operators-runtime-semantics-evaluation
+description: Logical Or Assignment Operator
+info: |
+    AssignmentExpression:
+      LeftHandSideExpression ||= AssignmentExpression
+
+    1. Let lref be the result of evaluating LeftHandSideExpression.
+    2. Let lval be ? GetValue(lref).
+    3. Let lbool be ! ToBoolean(lval).
+    4. If lbool is true, return lval.
+    5. Let rref be the result of evaluating AssignmentExpression.
+    6. Let rval be ? GetValue(rref).
+    7. Perform ? PutValue(lref, rval).
+    8. Return rval.
+
+---*/
+
+var value = undefined;
+assert.sameValue(value ||= 1, 1, "(value ||= 1) === 1; where value = undefined");
+
+value = null;
+assert.sameValue(value ||= 1, 1, "(value ||= 1) === 1; where value = null");
+
+value = false;
+assert.sameValue(value ||= 1, 1, "(value ||= 1) === 1; where value = false");
+
+value = 0;
+assert.sameValue(value ||= 1, 1, "(value ||= 1) === 1; where value = 0");
+
+value = -0;
+assert.sameValue(value ||= 1, 1, "(value ||= 1) === 1; where value = -0");
+
+value = NaN;
+assert.sameValue(value ||= 1, 1, "(value ||= 1) === 1; where value = NaN");
+
+value = "";
+assert.sameValue(value ||= 1, 1, '(value ||= 1) === 1; where value = ""');
+
+
+
+value = true;
+assert.sameValue(value ||= 1, true, "(value ||= 1) === true; where value = true");
+
+value = 2;
+assert.sameValue(value ||= 1, 2, "(value ||= 1) === 2; where value = 2");
+
+value = "test";
+assert.sameValue(value ||= 1, "test", '(value ||= 1) === "test"; where value = "test"');
+
+var sym = Symbol("");
+value = sym;
+assert.sameValue(value ||= 1, sym, "(value ||= 1) === Symbol(); where value = Symbol()");
+
+var obj = {};
+value = obj;
+assert.sameValue(value ||= 1, obj, "(value ||= 1) === {}; where value = {}");