js数组扁平化

1、 利用apply和concat转换

function reduceDimension(arr) {
    return Array.prototype.concat.apply([], arr);
}

2、reduce

let flat = [[1,2,3],[4,5,6],[7,8,9]].reduce((prev, next) => {
    return prev.concat(next)
});

3、多维数组递归降维

let arr = [[12], 4, [333, [4444, 5555]], [9, [111, 222]]];
    function arrayConcat(ary, point) {
        return [].concat.apply(point || [], ary);
    }

    function reduceDimesion(ary) {
        var arrays = arrayConcat(ary);
        let newAry = [];
        for (var i = 0, len = arrays.length; i < len; i++) {
            if({}.toString.call(arrays[i]) === '[object Array]'){
                newAry = arrayConcat(arrays[i], newAry);
            } else {
                newAry.push(arrays[i]);
            }
        }
        return newAry;
    }

// 扩展 ： n表示降多少维
function reduceDimesion(ary, n) {
        var arrays = arrayConcat(ary);
        let newAry = [];
        for (var i = 0, len = arrays.length; i < len; i++) {
            if({}.toString.call(arrays[i]) === '[object Array]' && n-- > 1){
                newAry = arrayConcat(arrays[i], newAry);
            } else {
                newAry.push(arrays[i]);
            }
        }
        return newAry;
    }