代码优化oooooo

function mosaicZero(var num) {
    //根据num拼接字符串zero,数字num是几字符串zero就有几个0.num取值范围0-16
    var zero = "";
    if (num == 0) zero = "0";
    if (num == 1) zero = "00";
    if (num == 2) zero = "000";
    if (num == 3) zero = "0000";
    if (num == 4) zero = "00000";
    if (num == 5) zero = "000000";
    if (num == 6) zero = "0000000";
    if (num == 7) zero = "00000000";
    if (num == 8) zero = "000000000";
    if (num == 9) zero = "0000000000";
    if (num == 10) zero = "00000000000";
    if (num == 11) zero = "000000000000";
    if (num == 12) zero = "0000000000000";
    if (num == 13) zero = "00000000000000";
    if (num == 14) zero = "000000000000000";
    if (num == 15) zero = "0000000000000000";
    if (num == 16) zero = "00000000000000000";
    return zero;
}

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ES6

function mosaicZero (num){
    return new Array(num + 1).fill(0);
}

---

var zero='';
function mosaicZero(num) {

for(var i=0;i<=num;i++){
    zero+='0';
}
return zero;

}

---

return "0".repeat(num);

等下，例子里是不是多了一个，num返回num+1个0？

那么

return "0".repeat(num+1);

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我去，最笨的办法 for 循环一次吧。。

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不知道你是不是只想得到0还是前面还有num，于是都写了，写的不好，轻喷

    function mosaicZero(num) {
        var zero = '';
        if (num < 16) {
            for (var i = 0; i < num; i++) {
                zero += '0' * num
            }
            zero = num.toString() + zero;
        }
        return zero;
    }

    console.log(mosaicZero(17))

    function mosaicZero(num) {
        var zero = '';
        if(num<16) {
            for(var i=0; i<num; i++) {
                zero += '0' * num
            }
        }
        return zero
    }
    console.log(mosaicZero(7));

---

function mosaicZero(num){
  if(typeof num === 'number'){
    return new Array(num +　1).join('0');
  } 
  
  return '';
}

主要利用了Array.prototype.join可以在数组间插入指定的字符串，所以先构建一个包含num + 1个元素的数组（需要+1才能在数组间产生num个间隔）。

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使用repeat方法：

function mosaicZero(num){
    if(num > -1 && num < 17){
        return "0".repeat(num + 1);
    }
    return "";
}

---

var num = 5;
var result = "00000000000000000".substr(0, num);