七大方法实现扁平化数组

// 使用栈
let toOne = function(arr) {
    let stack = [];
    let res = [];
    stack.push(arr);
    while (stack.length) {
        let temp = stack[stack.length - 1];
        if (temp.length) {
            let t = temp.shift();
            if (Array.isArray(t))
                stack.push(t);
            else
                res.push(t);
        } else
            stack.pop();
    }
    return res;
}

// reduce 递归
let toOne2 = function(arr) {
    return arr.reduce((pre, cur) => {
        return pre.concat(Array.isArray(cur) ? toOne2(cur) : cur);
    }, [])
}

// toString 和 split
let toOne3 = function(arr) {
    return arr.toString().split(',').map(item => {
        return Number(item);
    });
}

// join 和 split
let toOne4 = function(arr) {
    return arr.join(',').split(',').map(item => {
        return Number(item);
    })
}

// 递归
let toOne5 = function(arr) {
    let res = [];
    arr.map(item => {
        if (Array.isArray(item))
            res = res.concat(toOne5(item));
        else
            res.push(item);
    })
    return res;
}

// ... 扩展运算符
let toOne6 = function(arr) {
    while (arr.some(item => Array.isArray(item))) {
        arr = [].concat(...arr);
    }
    return arr;
}

console.log(toOne6([1, [2, [3, [4, 5.3, 6, [7]]]]]))



// ES10 Array.prototype.flat()
var arr1 = [1, 2, [3, 4]];
arr1.flat(); 
var arr2 = [1, 2, [3, 4, [5, 6]]];
arr2.flat();
var arr3 = [1, 2, [3, 4, [5, 6]]];
arr3.flat(2);//使用 Infinity 作为深度，展开任意深度的嵌套数组arr3.flat(Infinity);