题解 | #数组扁平化#

    const _flatten = arr => {
        let newArr = JSON.stringify(arr);
        let reg = /(\[|\])/g;
        let demo = newArr.replace(reg, '').split(',');
        for (let i = 0; i < demo.length; i++) {
            if (!(demo[i] instanceof Number)) {
                demo[i] = parseInt(demo[i])
            }
        }
        return demo;
    }

    const _flatten = arr => {
		let newArr = arr.flat(arr.length + 1);
		return newArr;
    }

用flat很简单，不知道为啥不通过。