为了方便记忆和称呼,ES2015之后的新知识点我们都统称ES6语法,就没必要去划分得那么细
ES7(2016)
Array.prototype.includes()
includes方法可以判断一个数组是否包含某个指定的值,如果存在返回true,否则false
const arr = ["es6", "es7", "es8", "es9"];
console.log(arr.includes("es5")); // false
console.log(arr.includes("es6")); // true
console.log(arr.includes("es6", 0)); // true
console.log(arr.includes("es6", 1)); // false
console.log(arr.includes("es6", -1)); // false
console.log(arr.includes("es6", -2)); // false
console.log(arr.includes("es6", -3)); // false
console.log(arr.includes("es6", -4)); // true
console.log(arr.includes("es6", -5)); // true
/*
arr.includes(valueFind,IndexFind)
valueFind,想要查询的值
includes的第二项参数为可选参数,即从IndexFind处开始查找,如果IndexFind为负数,则从末尾开始往前跳IndexFind绝对值个位置,然后开始往后找
*/
注意:includes()方法只能用于判断基本数据类型,如果是复杂数据类型,如对象,二维数组,则无法判断,并且能够判断NaN,null,undefined:
const arr1 = [1, 2, [3, 4], 5, {
name: "lucy" }, NaN, null, undefined];
console.log(arr1.includes([3, 4])); //false
console.log(