diff --git a/implementation-contributed/javascriptcore/stress/block-scope-redeclarations.js b/implementation-contributed/javascriptcore/stress/block-scope-redeclarations.js
new file mode 100644
index 0000000000..e244647d8d
--- /dev/null
+++ b/implementation-contributed/javascriptcore/stress/block-scope-redeclarations.js
@@ -0,0 +1,39 @@
+function shouldNotThrow(script) {
+  eval(script);
+}
+
+function shouldThrowSyntaxError(script) {
+    let error;
+    try {
+        eval(script);
+    } catch (e) {
+        error = e;
+    }
+
+    if (!(error instanceof SyntaxError))
+        throw new Error('Expected SyntaxError!');
+}
+
+shouldThrowSyntaxError('{ var x; let x; }');
+shouldThrowSyntaxError('{ { var x; } let x; }');
+shouldThrowSyntaxError('{ { { var x; } } let x; }');
+shouldThrowSyntaxError('{ let x; var x; }');
+shouldThrowSyntaxError('{ let x; { var x; } }');
+shouldThrowSyntaxError('{ let x; { { var x; } } }');
+
+shouldNotThrow('{ var x; { let x; } }');
+shouldNotThrow('{ var x; { { let x; } } }');
+shouldNotThrow('{ { let x; } var x; }');
+shouldNotThrow('{ { { let x; } } var x; }');
+
+shouldThrowSyntaxError('{ var x; const x = 0; }');
+shouldThrowSyntaxError('{ { var x; } const x = 0; }');
+shouldThrowSyntaxError('{ { { var x; } } const x = 0; }');
+shouldThrowSyntaxError('{ const x = 0; var x; }');
+shouldThrowSyntaxError('{ const x = 0; { var x; } }');
+shouldThrowSyntaxError('{ const x = 0; { { var x; } } }');
+
+shouldNotThrow('{ var x; { const x = 0; } }');
+shouldNotThrow('{ var x; { { const x = 0; } } }');
+shouldNotThrow('{ { const x = 0; } var x; }');
+shouldNotThrow('{ { { const x = 0; } } var x; }');
diff --git a/implementation-contributed/javascriptcore/stress/for-in-invalidate-context-weird-assignments.js b/implementation-contributed/javascriptcore/stress/for-in-invalidate-context-weird-assignments.js
new file mode 100644
index 0000000000..8c1a4fc93a
--- /dev/null
+++ b/implementation-contributed/javascriptcore/stress/for-in-invalidate-context-weird-assignments.js
@@ -0,0 +1,94 @@
+function assert(b) {
+    if (!b)
+        throw new Error("Bad");
+}
+
+function test(f) {
+    noInline(f);
+    for (let i = 0; i < 1000; ++i)
+        f();
+}
+
+function shouldThrowSyntaxError(script) {
+    let error;
+    try {
+        eval(script);
+    } catch (e) {
+        error = e;
+    }
+
+    if (!(error instanceof SyntaxError))
+        throw new Error('Expected SyntaxError!');
+}
+
+test(function() {
+    let o = {xx: 0};
+    for (let i in o) {
+        for (i in [0, 1, 2]) { }
+        assert(typeof i === "string");
+        assert(o[i] === undefined);
+    }
+});
+
+test(function() {
+    let o = {xx: 0};
+    for (let i in o) {
+        for ({i} of [{i: 0}]) { }
+        assert(typeof i === "number");
+        assert(o[i] === undefined);
+    }
+});
+
+test(function() {
+    let o = {xx: 0};
+    for (let i in o) {
+        ;({i} = {i: 0});
+        assert(typeof i === "number");
+        assert(o[i] === undefined);
+    }
+});
+
+test(function() {
+    let o = {xx: 0};
+    for (let i in o) {
+        ;([i] = [0]);
+        assert(typeof i === "number");
+        assert(o[i] === undefined);
+    }
+});
+
+test(function() {
+    let o = {xx: 0};
+    for (let i in o) {
+        ;({...i} = {a:20, b:30});
+        assert(typeof i === "object");
+        assert(o[i] === undefined);
+    }
+});
+
+test(function() {
+    let o = {xx: 0};
+    for (let i in o) {
+        eval("i = 0;");
+        assert(typeof i === "number");
+        assert(o[i] === undefined);
+    }
+});
+
+shouldThrowSyntaxError(
+    `function f() {
+        let o = {xx: 0};
+        for (let i in o) {
+            for (var i of [0]) { }
+        }
+    }`
+);
+
+shouldThrowSyntaxError(
+    `function f() {
+        let o = {xx: 0};
+        for (let i in o) {
+            var i = 0;
+        }
+    }`
+);
diff --git a/implementation-contributed/javascriptcore/stress/for-in-tests.js b/implementation-contributed/javascriptcore/stress/for-in-tests.js
new file mode 100644
index 0000000000..3282c5f1db
--- /dev/null
+++ b/implementation-contributed/javascriptcore/stress/for-in-tests.js
@@ -0,0 +1,199 @@
+function shouldThrowSyntaxError(script) {
+    let error;
+    try {
+        eval(script);
+    } catch (e) {
+        error = e;
+    }
+
+    if (!(error instanceof SyntaxError))
+        throw new Error('Expected SyntaxError!');
+}
+
+(function() {
+    // Iterate over an array with normal indexed properties.
+    var foo = function() {
+        var a = [1, 2, 3, 4, 5];
+        var sum = 0;
+        var result = "";
+        for (var p in a)
+            result += a[p];
+        return result;
+    };
+    noInline(foo);
+    for (var i = 0; i < 10000; ++i) {
+        if (foo() !== "12345")
+            throw new Error("bad result");
+    }
+    foo(null);
+})();
+(function() {
+    // Iterate over an object with normal non-indexed properties.
+    var foo = function() {
+        var o = {};
+        o.x = 1;
+        o.y = 2;
+        o.z = 3;
+        var result = "";
+        for (var p in o)
+            result += o[p];
+        return result;
+    };
+    noInline(foo);
+    for (var i = 0; i < 10000; ++i) {
+        if (foo() !== "123")
+            throw new Error("bad result");
+    }
+    foo(null);
+})();
+(function() {
+    // Iterate over an object with both indexed and non-indexed properties.
+    var foo = function() {
+        var o = {};
+        o.x = 1;
+        o.y = 2;
+        o.z = 3;
+        o[0] = 4;
+        o[1] = 5;
+        o[2] = 6;
+        var result = "";
+        for (var p in o)
+            result += o[p];
+        return result;
+    };
+    noInline(foo);
+    for (var i = 0; i < 10000; ++i) {
+        if (foo() != "456123")
+            throw new Error("bad result");
+    }
+    foo(null);
+})();
+(function() {
+    // Iterate over an array with both indexed and non-indexed properties.
+    var foo = function() {
+        var a = [4, 5, 6];
+        a.x = 1;
+        a.y = 2;
+        a.z = 3;
+        var result = "";
+        for (var p in a)
+            result += a[p];
+        return result;
+    };
+    noInline(foo);
+    for (var i = 0; i < 10000; ++i) {
+        if (foo() !== "456123")
+            throw new Error("bad result");
+    }
+    foo(null);
+})();
+(function() {
+    var foo = function(a, b) {
+        for (var p in b) {
+            var f1 = a[p];
+            var f2 = b[p];
+            if (f1 === f2)
+                continue;
+            a[p] = b[p];
+        }
+    };
+    noInline(foo);
+    for (var i = 0; i < 10000; ++i) {
+        var o1 = {};
+        var o2 = {};
+        o2.x = 42;
+        o2.y = 53;
+        foo(o1, o2);
+        if (o1.x !== o2.x)
+            throw new Error("bad result: " + o1.x + "!==" + o2.x);
+        if (o1.y !== o2.y)
+            throw new Error("bad result: " + o1.y + "!==" + o2.y);
+    }
+})();
+
+(function() {
+    var foo = function(a, b) {
+        for (var p = b in a) {}
+        return p;
+    };
+    noInline(foo);
+    for (var i = 0; i < 10000; ++i) {
+        var expected = 'expected-result';
+        var result = foo({}, expected);
+        if (expected !== result)
+            throw new Error("bad result: " + result + "!==" + expected);
+    }
+    for (var i = 0; i < 10000; ++i) {
+        var expected = 'a';
+        var result = foo({a:'abcd'}, expected);
+        if (expected !== result)
+            throw new Error("bad result: " + result + "!==" + expected);
+    }
+    for (var i = 0; i < 10000; ++i) {
+        var expected = 'b';
+        var result = foo({a:'abcd', b: 'bcde'}, expected);
+        if (expected !== result)
+            throw new Error("bad result: " + result + "!==" + expected);
+    }
+
+    for (var i = 0; i < 10000; ++i) {
+        var expected = 'c';
+        var o = {a:'abcd', b: 'bcde'};
+        o.c = 'cdef';
+        var result = foo(o, expected);
+        if (expected !== result)
+            throw new Error("bad result: " + result + "!==" + expected);
+    }
+})();
+
+(function() {
+    var boo = function () { return 'expected-result'; };
+    var foo = function(a) {
+        for (var p = boo() in a) {}
+        return p;
+    };
+    noInline(foo);
+    for (var i = 0; i < 10000; ++i) {
+        var expected = 'expected-result';
+        var result = foo({});
+        if (expected !== result)
+            throw new Error("bad result: " + result + "!==" + expected);
+    }
+})();
+
+shouldThrowSyntaxError(
+    `function foo(a, b) {
+        {
+            let p = 'some-value';
+            for (var p = b in a) {}
+        }
+    }`
+);
+
+(function() {
+    var foo = function(a, b, c) {
+        for (var p = b + c in a) {}
+        return p;
+    };
+    noInline(foo);
+    for (var i = 0; i < 10000; ++i) {
+        var expected = 'expected-result';
+        var result = foo({}, 'expected', '-result');
+        if (expected !== result)
+            throw new Error("bad result: " + result + "!==" + expected);
+    }
+})();
+
+shouldThrowSyntaxError(
+    `function foo() {
+        'use strict';
+        for (var i = 0 in {}) {}
+    }`
+);
+
+shouldThrowSyntaxError(
+    `function foo() {
+        const i = 10;
+        for (var i = 0 in {}) {}
+    }`
+);
diff --git a/implementation-contributed/javascriptcore/stress/json-stringify-string-builder-overflow.js b/implementation-contributed/javascriptcore/stress/json-stringify-string-builder-overflow.js
new file mode 100644
index 0000000000..240c4f3c23
--- /dev/null
+++ b/implementation-contributed/javascriptcore/stress/json-stringify-string-builder-overflow.js
@@ -0,0 +1,29 @@
+//@ slow!
+//@ skip if $architecture != "arm64" and $architecture != "x86-64"
+
+var exception;
+try {
+    var str = JSON.stringify({
+        'a1': {
+            'a2': {
+                'a3': {
+                    'a4': {
+                        'a5': {
+                            'a6': 'AAAAAAAAAA'
+                        }
+                    }
+                }
+            }
+        }
+    }, function (key, value) {
+        var val = {
+            'A': true,
+        };
+        return val;
+    }, 1);
+} catch (e) {
+    exception = e;
+}
+
+if (exception != "Error: Out of memory")
+    throw "FAILED";
diff --git a/implementation-contributed/javascriptcore/stress/pow-expects-update-expression-on-lhs.js b/implementation-contributed/javascriptcore/stress/pow-expects-update-expression-on-lhs.js
new file mode 100644
index 0000000000..c255259f3f
--- /dev/null
+++ b/implementation-contributed/javascriptcore/stress/pow-expects-update-expression-on-lhs.js
@@ -0,0 +1,96 @@
+function testSyntax(script) {
+    try {
+        eval(script);
+    } catch (error) {
+        if (error instanceof SyntaxError)
+            throw new Error("Bad error: " + String(error));
+    }
+}
+
+function testSyntaxError(script, message) {
+    var error = null;
+    try {
+        eval(script);
+    } catch (e) {
+        error = e;
+    }
+    if (!error)
+        throw new Error("Expected syntax error not thrown");
+
+    if (String(error) !== message)
+        throw new Error("Bad error: " + String(error));
+}
+
+{
+    let tokens = [
+        '-',
+        '+',
+        '~',
+        '!',
+        'typeof',
+        'void',
+        'delete',
+    ];
+
+    for (let token of tokens) {
+        testSyntaxError(`
+        function pow(a, b)
+        {
+            return ${token} a ** b;
+        }
+        `, `SyntaxError: Unexpected token '**'. Ambiguous unary expression in the left hand side of the exponentiation expression; parentheses must be used to disambiguate the expression.`);
+    }
+}
+
+{
+    let tokens = [
+        '-',
+        '+',
+        '~',
+        '!',
+        'typeof',
+        'void',
+        'delete',
+    ];
+
+    for (let token of tokens) {
+        testSyntax(`
+        function pow(a, b)
+        {
+            return (${token} a) ** b;
+        }
+        `);
+    }
+}
+
+{
+    let tokens = [
+        '++',
+        '--',
+    ];
+
+    for (let token of tokens) {
+        testSyntax(`
+        function pow(a, b)
+        {
+            return ${token} a ** b;
+        }
+        `);
+    }
+}
+
+{
+    let tokens = [
+        '++',
+        '--',
+    ];
+
+    for (let token of tokens) {
+        testSyntax(`
+        function pow(a, b)
+        {
+            return a ${token} ** b;
+        }
+        `);
+    }
+}
diff --git a/implementation-contributed/javascriptcore/stress/property-name-enumerator-should-cache-structure-after-getting-property-names.js b/implementation-contributed/javascriptcore/stress/property-name-enumerator-should-cache-structure-after-getting-property-names.js
new file mode 100644
index 0000000000..27c4192e27
--- /dev/null
+++ b/implementation-contributed/javascriptcore/stress/property-name-enumerator-should-cache-structure-after-getting-property-names.js
@@ -0,0 +1,11 @@
+function foo(){
+    o = Error();
+    for (var s in o) {
+        o[s];
+        o = Error();
+    }
+}
+noInline(foo);
+
+for(var i = 0; i < 100; i++)
+    foo();
diff --git a/implementation-contributed/javascriptcore/stress/string-16bit-repeat-overflow.js b/implementation-contributed/javascriptcore/stress/string-16bit-repeat-overflow.js
new file mode 100644
index 0000000000..bc724fbf62
--- /dev/null
+++ b/implementation-contributed/javascriptcore/stress/string-16bit-repeat-overflow.js
@@ -0,0 +1,9 @@
+var exception;
+try {
+    print('\ud000'.repeat(2**30));
+} catch (e) {
+    exception = e;
+}
+
+if (exception != "Error: Out of memory")
+    throw "FAILED";
diff --git a/implementation-contributed/javascriptcore/stress/string-overflow-createError.js b/implementation-contributed/javascriptcore/stress/string-overflow-createError.js
new file mode 100644
index 0000000000..01d95ad622
--- /dev/null
+++ b/implementation-contributed/javascriptcore/stress/string-overflow-createError.js
@@ -0,0 +1,11 @@
+var exception;
+try {
+    bar = '2.3023e-320'
+    foo = bar.padEnd(2147483644, 1);
+    foo(true, 1).value;
+} catch (e) {
+    exception = e;
+}
+
+if (exception != "Error: Out of memory")
+    throw "FAILED";