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includes() true false
const array1 = [1, 2, 3];
console.log(array1.includes(2));
// Expected output: true
const pets = ["cat", "dog", "bat"];
console.log(pets.includes("cat"));
// Expected output: true
console.log(pets.includes("at"));
// Expected output: false
includes(searchElement)
includes(searchElement, fromIndex)
searchElementfromIndex fromIndex < 0 fromIndex + array.lengthfromIndex < -array.length fromIndex 0fromIndex >= array.length false fromIndex fromIndex searchElement true
includes() searchElement 0 -0 0 false 0 NaN
[1, 2, 3].includes(2); // true
[1, 2, 3].includes(4); // false
[1, 2, 3].includes(3, 3); // false
[1, 2, 3].includes(3, -1); // true
[1, 2, NaN].includes(NaN); // true
["1", "2", "3"].includes(3); // false
fromIndex false
const arr = ["a", "b", "c"];
arr.includes("c", 3); // false
arr.includes("c", 100); // false
fromIndex searchElement 0
// 3
// fromIndex -100
// 3 + (-100) = -97
const arr = ["a", "b", "c"];
arr.includes("a", -100); // true
arr.includes("b", -100); // true
arr.includes("c", -100); // true
arr.includes("a", -2); // false
undefined true
console.log([1, , 3].includes(undefined)); // true
includes() this length
const arrayLike = {
length: 3,
0: 2,
1: 3,
2: 4,
};
console.log(Array.prototype.includes.call(arrayLike, 2));
// true
console.log(Array.prototype.includes.call(arrayLike, 1));
// false
| ECMAScript 2027 LanguageSpecification # sec-array.prototype.includes |
ArrayArray.prototype.at()Array.prototype.concat()Array.prototype.copyWithin()Array.prototype.entries()Array.prototype.every()Array.prototype.fill()Array.prototype.filter()Array.prototype.find()Array.prototype.findIndex()findLast()Array.prototype.findLastIndex()Array.prototype.flat()Array.prototype.flatMap()Array.prototype.forEach()Array.prototype.includes()Array.prototype.indexOf()Array.prototype.join()Array.prototype.keys()Array.prototype.lastIndexOf()Array.prototype.map()Array.prototype.pop()Array.prototype.push()Array.prototype.reduce()Array.prototype.reduceRight()Array.prototype.reverse()Array.prototype.shift()Array.prototype.slice()Array.prototype.some()Array.prototype.sort()Array.prototype.splice()Array.prototype.toLocaleString()Array.prototype.toReversed()Array.prototype.toSorted()Array.prototype.toSpliced()Array.prototype.toString()Array.prototype.unshift()Array.prototype.values()Array.prototype.with()Array.prototype[Symbol.iterator]()Object/FunctionObject.prototype.__defineGetter__()Object.prototype.__defineSetter__()Object.prototype.__lookupGetter__()Object.prototype.__lookupSetter__()Object.prototype.hasOwnProperty()Object.prototype.isPrototypeOf()Object.prototype.propertyIsEnumerable()Object.prototype.toLocaleString()Object.prototype.toString()Object.prototype.valueOf()| Web Proxy Viewer | New URL | Original Page |