JavaScript Array `includes()`
The Array#includes() method returns true if the array contains a given element, or false otherwise.
const arr = ['a', 'b', 'c'];
arr.includes('b'); // true
arr.includes('z'); // false
arr.includes(1); // falseEquality Comparison
The includes() method uses the "SameValueZero" algorithm for determining if two values are equal. For almost all
cases, "SameValueZero" is equivalent to strict equality using ===. In particular,
includes() does not do any type coercion.
const arr = ['1', '2', '3'];
arr.includes('1'); // true
arr.includes(1); // falseThe includes() only treats two objects as equal if they are the same reference:
const obj1 = { name: 'Jean-Luc Picard' };
const obj2 = { name: 'Jean-Luc Picard' };
const arr = [obj1];
arr.includes(obj1); // true
arr.includes(obj2); // falseThe only difference is how SameValueZero handles NaN. In JavaScript, NaN !== NaN. However, includes() can correctly find NaN and Number.NaN in an
array.
const arr = [NaN];
arr.includes(NaN); // true
arr.includes(Number.NaN); // true
arr[0] === NaN; // falseEnvironment Support
The includes() method was introduced in ES2016, which makes
it a relatively new feature. In particular, no version Internet Explorer supports includes(). If you expect your
JavaScript to run in Internet Explorer or versions of Node.js before 5.0.0, you should use indexOf(), which enjoys
better browser support and is equivalent except for NaN.