如何在JavaScript中输出带有前导零的数字

本文翻译自：How to output numbers with leading zeros in JavaScript [duplicate]

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Closed 7 years ago . 7年前关闭。

Possible Duplicate: 可能重复：
How can I create a Zerofilled value using JavaScript? 如何使用JavaScript创建零填充值？

I can round to x amount of decimal places with math.round but is there a way to round left of the decimal? 我可以用math.round舍入到小数位数的x位数，但是有没有办法舍入到小数点左边？ for example 5 becomes 05 if I specify 2 places 例如，如果我指定2个位置，则5变为05

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#1楼

参考：https://stackoom.com/question/Ca7U/如何在JavaScript中输出带有前导零的数字

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#2楼

You could extend the Number object: 您可以扩展Number对象：

Number.prototype.pad = function(size) {
    var s = String(this);
    while (s.length < (size || 2)) {s = "0" + s;}
    return s;
}

Examples: 例子：

(9).pad();  //returns "09"

(7).pad(3);  //returns "007"

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#3楼

NOTE : Potentially outdated. 注意 ：可能已过时。 ECMAScript 2017 includes String.prototype.padStart ECMAScript 2017包含String.prototype.padStart

You're asking for zero padding? 您是否要求零填充？ Not really rounding. 不是真正的舍入。 You'll have to convert it to a string since numbers don't make sense with leading zeros. 您必须将其转换为字符串，因为数字对于前导零没有意义。 Something like this... 像这样

function pad(num, size) {
    var s = num+"";
    while (s.length < size) s = "0" + s;
    return s;
}

Or if you know you'd never be using more than X number of zeros this might be better. 或者，如果您知道您永远不会使用超过X个零的数字，那可能会更好。 This assumes you'd never want more than 10 digits. 这假设您永远不要超过10位数字。

function pad(num, size) {
    var s = "000000000" + num;
    return s.substr(s.length-size);
}

If you care about negative numbers you'll have to strip the "-" and readd it. 如果您关心负数，则必须去除“-”并读取它。

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#4楼

UPDATE: Small one-liner function using the ES2017 String.prototype.padStart method: 更新：使用ES2017 String.prototype.padStart方法的小型一线函数：

 function zeroPad(num, places) { return String(num).padStart(places, '0') } console.log(zeroPad(5, 2)); // "05" console.log(zeroPad(5, 4)); // "0005" console.log(zeroPad(5, 6)); // "000005" console.log(zeroPad(1234, 2)); // "1234" 

Another ES5 approach: ES5的另一种方法：

function zeroPad(num, places) {
  var zero = places - num.toString().length + 1;
  return Array(+(zero > 0 && zero)).join("0") + num;
}

zeroPad(5, 2); // "05"
zeroPad(5, 4); // "0005"
zeroPad(5, 6); // "000005"
zeroPad(1234, 2); // "1234" :)

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#5楼

Just for fun (I had some time to kill), a more sophisticated implementation which caches the zero-string: 只是为了好玩（我有时间消磨时间），这是一个更复杂的实现，它缓存零字符串：

pad.zeros = new Array(5).join('0');
function pad(num, len) {
    var str = String(num),
        diff = len - str.length;
    if(diff <= 0) return str;
    if(diff > pad.zeros.length)
        pad.zeros = new Array(diff + 1).join('0');
    return pad.zeros.substr(0, diff) + str;
}

If the padding count is large and the function is called often enough, it actually outperforms the other methods... 如果填充数很大并且经常调用该函数，则它实际上胜过其他方法...

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#6楼

From https://gist.github.com/1180489 从https://gist.github.com/1180489

function pad(a,b){return(1e15+a+"").slice(-b)}

With comments: 有评论：

function pad(
  a, // the number to convert 
  b // number of resulting characters
){
  return (
    1e15 + a + // combine with large number
    "" // convert to string
  ).slice(-b) // cut leading "1"
}