What is the difference between JavaScript's equality operators?

Angelos Chalaris · Aug 6, 2020 ·

JavaScript, Type, Comparison

JavaScript provides two equality operators used for comparisons:

  • The double equals (==), also known as the loose equality operator
  • The triple equals (===), also known as the strict equality operator

The key difference between the two is that the triple equals (===) operator compares both type and value, whereas the double equals (==) operator uses type coercion so that both operands are of the same type, then compares only the resulting values.

Here are some examples to clear up any confusion:

const num = 0;
const str = '0';
const obj = new String(0);
const bool = false;
const undef = undefined;
const nil = null;

console.dir([
  num == str,     // 0 == 0, true
  num == bool,    // 0 == 0, true
  str == obj,     // '0' == '0', true
  obj == num,     // 0 == 0, true
  bool == str,    // 0 == 0, true
  bool == obj,    // 0 == 0, true
  bool == nil,    // false
  undef == nil,   // true
  undef == bool,  // false
]);

console.dir([
  num === str,     // types don't match, false
  num === bool,    // types don't match, false
  str === obj,     // types don't match, false
  obj === num,     // types don't match, false
  bool === str,    // types don't match, false
  bool === obj,    // types don't match, false
  bool === nil,    // types don't match, false
  undef === nil,   // types don't match, false
  undef === bool,  // types don't match, false
]);

As you can see from the examples above, using the triple equals (===) operator is far more predictable and intuitive than the double equals (==) operator. Therefore, we recommend you use the triple equals (===) operator for most cases, unless you are entirely certain you want type coercion to be applied to the comparison's operands.

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