test262/test/language/expressions/logical-assignment/lgcl-nullish-assignment-operator-lhs-before-rhs.js

// 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.
features: [logical-assignment-operators]

---*/

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(TypeError, 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");