题目描述：

<script>
        const num = [1,2,3,4]
        const out = (function(num,m,n){
            if(num.length !== m*n){
                return []
            }
            const newarr = []

            for(let i =0;i<m;i++){
                newarr.push(num.slice(i*n,(i+1)*n))
            }
            return newarr
            

        })(num,2,2)

        console.log(out)
    </script>

不使用String类属性的方法

/**
 * @param {number[]} original
 * @param {number} m
 * @param {number} n
 * @return {number[][]}
 */
var construct2DArray = function(original, m, n) {
    const newarr = []
    if(original.length !== m*n){
        return newarr
    }
    for(let i =0;i<original.length;){

        for(let j=0;j<m;j++){
            let teparr = []
            for(let k=0;k<n;k++){
                teparr.push(original[i])
                i++
            }
            newarr.push(teparr)
        }
    }
    return newarr
    
};