Object.is()

Object.is() is a static method that compares two values for equality, returning true if they are equal and false otherwise.

It differs from other equality operators such as == and === in its treatment of special values like NaN and -0.

Syntax

Object.is(value1, value2);

Parameter

• value1: The first value to compare.

• value2: The second value to compare.

Return Value

A Boolean, true or false, indicating whether the two values are equal.

Examples

Object.is(1, 1); // true
Object.is("hello", "hello"); // true
Object.is("1", 1); // false
Object.is(NaN, NaN); // true
Object.is(0, -0); // false

In the above example, the first three comparisons are straightforward and return expected results. The fourth comparison is unique to Object.is(), which treats two NaN values as equal. The fifth comparison is also unique to Object.is(), which distinguishes between positive and negative zero.

Ecmascript Version & Browser support

Object.is() was added in ECMAScript 6 (ES6) and is supported by most modern browsers, including Chrome, Firefox, Edge, Safari, and Opera.

Notes

• Object.is() is not intended to be a replacement for the == or === operators. It is only intended to provide a more precise way to compare values in certain cases.

• Object.is() does not perform type coercion. It treats values of different types as unequal, except in the case of NaN and -0.

• Object.is() is useful for comparing NaN values, since NaN is the only value that is not equal to itself using the == and === operators.

• Object.is() is also useful for distinguishing between positive and negative zero. This can be important in some mathematical calculations.

• Object.is() is not supported in older browsers, such as Internet Explorer. In those cases, a polyfill can be used to provide similar functionality.

Exercises

1. Write a function that uses Object.is() to compare two arrays of primitive values for equality.

function isEqualArray(arr1, arr2) {
  if (arr1.length !== arr2.length) {
    return false;
  }
  for (let i = 0; i < arr1.length; i++) {
    if (!Object.is(arr1[i], arr2[i])) {
      return false;
    }
  }
  return true;
}

2. Write a function that takes an array of numbers and returns the sum of those numbers, treating positive and negative zero as separate values, using Object.is().

function sum(numbers) {
  let total = 0;
  for (let number of numbers) {
    if (Object.is(number, 0) && 1 / number === -Infinity) {
      total -= 0;
    } else {
      total += number;
    }
  }
  return total;
}

3. Write a function that returns true if a given value is NaN and false otherwise, using Object.is().

function isNan(value) {
  return Object.is(value, NaN);
}