js数组高阶函数之includes()方法总结

let myArray = []; // 创建一个空数组
let myArray = [1, 2, 3]; // 创建一个包含三个数值的数组
let myArray = new Array(); // 用构造函数创建一个空数组
let myArray = new Array(1, 2, 3); // 用构造函数创建一个包含三个数值的数组

 let myArray = [1, 2, 3];console.log(myArray.length); // 输出 3

let myArray = [1, 2, 3];
console.log(myArray[0]); // 输出 1
console.log(myArray[1]); // 输出 2
console.log(myArray[2]); // 输出 3

let myArray = [1, 2, 3];
myArray[1] = 4;
console.log(myArray); // 输出 [1, 4, 3]

let myArray = [1, 2, 3];
delete myArray[1];
console.log(myArray); // 输出 [1, 3]

let myArray = [1, 2, 3];
myArray.push(4);
console.log(myArray); // 输出 [1, 2, 3, 4]

let myArray = [1, 2, 3];
myArray.pop();
console.log(myArray); // 输出 [1, 2]

 array.includes(searchElement[, fromIndex])

const numbers = [1, 2, 3, 4, 5];
console.log(numbers.includes(3)); 
console.log(numbers.includes(6)); 

const fruits = ['长生界', '神墓', '遮天'];
console.log(fruits.includes('遮天')); 
console.log(fruits.includes('完美世界')); 

const users = [
  { name: '叶天帝', age: 225 },
  { name: '石昊', age: 130 },
  { name: '辰南', age: 135 }
];
const user = { name: '石昊', age: 130 };
console.log(users.includes(user)); // false

const users = [
  { name: '叶天帝', age: 225 },
  { name: '石昊', age: 130 },
  { name: '辰南', age: 135 }
];
const user = { name: '石昊', age: 130 };
const isUserIncluded = users.some(u => u.name === user.name && u.age === user.age);
console.log(isUserIncluded); //true

if (!Array.prototype.includes) {
    Array.prototype.includes = function(searchElement /*, fromIndex*/ ) {
        'use strict';
        var O = Object(this);
        var len = parseInt(O.length) || 0;
        if (len === 0) {
            return false;
        }
        var n = parseInt(arguments[1]) || 0;
        var k;
        if (n >= 0) {
            k = n;
        } else {
            k = len + n;
            if (k < 0) {
                k = 0;
            }
        }
        while (k < len) {
            var currentElement = O[k];
            if (searchElement === currentElement ||
                (searchElement !== searchElement && currentElement !== currentElement)) {
                return true;
            }
            k++;
        }
        return false;
    };
}