Object.is() - JavaScript 编辑

The Object.is() method determines whether two values are the same value.

Syntax

Object.is(value1, value2);

Parameters

value1

The first value to compare.

value2

The second value to compare.

Return value

A Boolean indicating whether or not the two arguments are the same value.

Description

Object.is() determines whether two values are the same value. Two values are the same if one of the following holds:

• both undefined
• both null
• both true or both false
• both strings of the same length with the same characters in the same order
• both the same object (meaning both values reference the same object in memory)
• both numbers and
  • both +0
  • both -0
  • both NaN
  • or both non-zero and both not NaN and both have the same value

This is not the same as being equal according to the == operator. The == operator applies various coercions to both sides (if they are not the same Type) before testing for equality (resulting in such behavior as "" == false being true), but Object.is doesn't coerce either value.

This is also not the same as being equal according to the === operator. The === operator (and the == operator as well) treats the number values -0 and +0 as equal and treats Number.NaN as not equal to NaN.

Examples

Using Object.is

Object.is('foo', 'foo');     // true
Object.is(window, window);   // true

Object.is('foo', 'bar');     // false
Object.is([], []);           // false

var foo = { a: 1 };
var bar = { a: 1 };
Object.is(foo, foo);         // true
Object.is(foo, bar);         // false

Object.is(null, null);       // true

// Special Cases
Object.is(0, -0);            // false
Object.is(-0, -0);           // true
Object.is(NaN, 0/0);         // true

Polyfill

if (!Object.is) {
  Object.defineProperty(Object, "is", {
    value: function (x, y) {
      // SameValue algorithm
      if (x === y) { // Steps 1-5, 7-10
        // Steps 6.b-6.e: +0 != -0
        return x !== 0 || 1 / x === 1 / y;
      } else {
        // Step 6.a: NaN == NaN
        return x !== x && y !== y;
      }
    }
  });
}

Specifications

Browser compatibility

BCD tables only load in the browser

See also

• Equality comparisons and sameness — a comparison of all three built-in sameness facilities