浅谈JS数组内置遍历方法有哪些和区别

const array1 = ['a', 'b', 'c'];
array1.forEach(element => console.log(element));

    const array1 = [1, 4, 9, 16];
    const map1 = array1.map(x => x * 2);
    console.log(map1);  //[2, 8, 18, 32]

    var arr1 = [1, 2, [3, 4]];
    arr1.flatMap(x => x);    //[1, 2, 3, 4]
    var arr1 = [1, 2, 3, 4];
    arr1.flatMap(x => [[x * 2]]);   // [[2], [4], [6], [8]]

    const result = words.filter(word => word.length > 6);
    console.log(result)   //["exuberant", "destruction", "present"]
some（）函数（ES6）
    遍历数组中是否有符合条件的元素，返回值为Boolean值
    这个它只要找到一个符合条件的，就返回 true。
    var arr = [
     { id: 1, name: '买笔', done: true },
     { id: 2, name: '买笔记本', done: true },
     { id: 3, name: '练字', done: false }
    ]
    
    var bool = arr.some(function (item, index) {
     return item.done
    })
    console.log(bool)    // true

    var arr = [
        { id: 1, name: '买笔', done: true },
        { id: 2, name: '买笔记本', done: true },
        { id: 3, name: '练字', done: false }
    ]
    var bool = arr.every((item, index) => {
        return item.done
    })
    console.log(bool)    // false

    var arr = [1, 1, 2, 2, 3, 3, 4, 5, 6]
    var num = arr.find( (item, index) => {
        return item === 3
    })
    console.log(num)   //  3

    var arr = [1, 1, 2, 2, 3, 3, 4, 5, 6]
    var num = arr.findIndex(item => {
        return item === 3
    })
    console.log(num)   //  4