如何在 JavaScript 中输出带前导零的数字
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How to output numbers with leading zeros in JavaScript
提问by chris
I can round to x amount of decimal places with math.round but is there a way to round left of the decimal? for example 5 becomes 05 if I specify 2 places
我可以用 math.round 四舍五入到 x 的小数位，但有没有办法四舍五入小数点的左边？例如，如果我指定 2 个位置，则 5 变为 05
回答by InfinitiesLoop
NOTE: Potentially outdated. ECMAScript 2017 includes String.prototype.padStart
注意：可能已经过时。ECMAScript 2017 包含String.prototype.padStart
You're asking for zero padding? Not really rounding. You'll have to convert it to a string since numbers don't make sense with leading zeros. Something like this...
你要求零填充？不是真的四舍五入。您必须将其转换为字符串，因为数字对前导零没有意义。像这样的东西...
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. This assumes you'd never want more than 10 digits.
或者，如果您知道您永远不会使用超过 X 个零，这可能会更好。这假设您永远不会想要超过 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，则必须去掉“-”并阅读它。
回答by Mild Fuzz
You could extend the Numberobject:
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"
回答by CMS
UPDATE:Small one-liner function using the ES2017 String.prototype.padStartmethod:
更新：使用 ES2017String.prototype.padStart方法的小型单行函数：
const zeroPad = (num, places) => 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:
另一种 ES5 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" :)
回答by dave1010
From https://gist.github.com/1180489
来自https://gist.github.com/1180489
function pad(a,b){return(1e15+a+"").slice(-b)}
With comments:
附评论：
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"
}
回答by ithinc
function zfill(num, len) {return (Array(len).join("0") + num).slice(-len);}
回答by Christoph
Just for fun (I had some time to kill), a more sophisticated implementation which caches the zero-string:
只是为了好玩（我有一些时间来消磨时间），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...
如果填充计数很大并且该函数被足够频繁地调用，它实际上优于其他方法......
