JSTests/test262/test/language/expressions/compound-assignment/S11.13.2_A4.4_T1.3.js

// Copyright 2009 the Sputnik authors.  All rights reserved.
// This code is governed by the BSD license found in the LICENSE file.

/*---
info: The production x += y is the same as x = x + y
es5id: 11.13.2_A4.4_T1.3
description: Type(x) and Type(y) vary between Null and Undefined
---*/

var x;

//CHECK#1
x = null;
x += undefined;
if (isNaN(x) !== true) {
  $ERROR('#1: x = null; x += undefined; x === Not-a-Number. Actual: ' + (x));
}

//CHECK#2
x = undefined;
x += null;
if (isNaN(x) !== true) {
  $ERROR('#2: x = undefined; x += null; x === Not-a-Number. Actual: ' + (x));
}

//CHECK#3
x = undefined;
x += undefined;
if (isNaN(x) !== true) {
  $ERROR('#3: x = undefined; x += undefined; x === Not-a-Number. Actual: ' + (x));
}

//CHECK#4
x = null;
x += null;
if (x !== 0) {
  $ERROR('#4: x = null; x += null; x === 0. Actual: ' + (x));
}