使用ECMAScript 6方法String#repeat，一个pad函数就像这样简单:

String.prototype.padLeft = function(char, length) {
    return char.repeat(Math.max(0, length - this.length)) + this;
}

字符串#repeat目前仅在Firefox和Chrome中支持。对于其他实现，可以考虑以下简单的polyfill:

String.prototype.repeat = String.prototype.repeat || function(n){
    return n<=1 ? this : (this + this.repeat(n-1));
}

以下是我的看法:

我不太确定它的性能，但我发现它比我在这里看到的其他选项更具可读性……

var replicate = function(len, char) {
  return Array(len + 1).join(char || ' ');
};

var padr = function(text, len, char) {
  if (text.length >= len)
    return text;
  return text + replicate(len-text.length, char);
};

包括所有选项

function padding(stringToBePadded, paddingCharacter, totalLength, padLeftElseRight){
    //will pad any string provided in first argument, with padding character provide in 2nd argument and truncate to lenght provided in third argument, padding left if 4th argument true or undefined, right if false. 
    // i.e. padding("lode","x","10")  -->  "xxxxxxlode"
    // i.e. padding("lode","x","10",true)  -->  "xxxxxxlode"
    // i.e. padding("lode","x","10",false)  -->  "lodexxxxxx"
    // i.e. padding("12","0","5")  -->  "00012"
    {
        padLeftElseRight = typeof padLeftElseRight !== 'undefined' ? padLeftElseRight : true;
    }
    if (stringToBePadded.length > totalLength){
        // console.log("string too long to be padded");
        return stringToBePadded;
    }
    var paddingString = paddingCharacter.repeat(totalLength);//make long string of padding characters
    if ( padLeftElseRight){
        return String(paddingString+stringToBePadded).slice(-totalLength);
    }else{ 
        return String(stringToBePadded+paddingString).slice(0,totalLength); 
    }
}

有点晚了，但我还是想分享一下。我发现向Object添加一个原型扩展很有用。这样我就可以填充数字和字符串，向左或向右。我有一个模块与类似的实用程序，我包括在我的脚本。

// include the module in your script, there is no need to export
var jsAddOns = require('<path to module>/jsAddOns');

~~~~~~~~~~~~ jsAddOns.js ~~~~~~~~~~~~

/* 
 * method prototype for any Object to pad it's toString()
 * representation with additional characters to the specified length
 *
 * @param padToLength required int
 *     entire length of padded string (original + padding)
 * @param padChar optional char
 *     character to use for padding, default is white space
 * @param padLeft optional boolean
 *     if true padding added to left
 *     if omitted or false, padding added to right
 *
 * @return padded string or
 *     original string if length is >= padToLength
 */
Object.prototype.pad = function(padToLength, padChar, padLeft) {    

    // get the string value
    s = this.toString()

    // default padToLength to 0
    // if omitted, original string is returned
    padToLength = padToLength || 0;

    // default padChar to empty space
    padChar = padChar || ' ';


    // ignore padding if string too long
    if (s.length >= padToLength) {
        return s;
    }

    // create the pad of appropriate length
    var pad = Array(padToLength - s.length).join(padChar);

    // add pad to right or left side
    if (padLeft) {
        return pad  + s;        
    } else {
        return s + pad;
    }
};

函数 var _padLeft = function(paddingString, width, replacementChar) { paddingString返回。长度>=宽度?paddingString: _padLeft(replacementChar + paddingString, width, replacementChar || ' '); }; 字符串的原型 String.prototype.padLeft = function(width, replacementChar) { 返回。长度>=宽度?this. tostring ():(replacementChar + this)。padLeft(width, replacementChar || ' '); }; 片 ('00000' + paddingString).slice(-5)

对于这样的东西，我可能会在需要它的地方创建一个单行函数:

var padleft = (s,c,len) => { while(s.length < len) s = c + s; return s; }

例子:

> console.log( padleft( '110', '0', 8) );
> 00000110