http://www.webtoolkit.info/javascript_pad.html

/**
*
*  JavaScript string pad
*  http://www.webtoolkit.info/
*
**/

var STR_PAD_LEFT = 1;
var STR_PAD_RIGHT = 2;
var STR_PAD_BOTH = 3;

function pad(str, len, pad, dir) {

    if (typeof(len) == "undefined") { var len = 0; }
    if (typeof(pad) == "undefined") { var pad = ' '; }
    if (typeof(dir) == "undefined") { var dir = STR_PAD_RIGHT; }

    if (len + 1 >= str.length) {

        switch (dir){

            case STR_PAD_LEFT:
                str = Array(len + 1 - str.length).join(pad) + str;
            break;

            case STR_PAD_BOTH:
                var padlen = len - str.length;
                var right = Math.ceil( padlen / 2 );
                var left = padlen - right;
                str = Array(left+1).join(pad) + str + Array(right+1).join(pad);
            break;

            default:
                str = str + Array(len + 1 - str.length).join(pad);
            break;

        } // switch

    }

    return str;
}

可读性更强。

@Daniel LaFavers回答的一个变体。

var mask = function (background, foreground) {
  bg = (new String(background));
  fg = (new String(foreground));
  bgl = bg.length;
  fgl = fg.length;
  bgs = bg.substring(0, Math.max(0, bgl - fgl));
  fgs = fg.substring(Math.max(0, fgl - bgl));
  return bgs + fgs;
};

例如:

mask('00000', 11  );   // '00011'
mask('00011','00' );   // '00000'
mask( 2     , 3   );   // '3'
mask('0'    ,'111');   // '1'
mask('fork' ,'***');   // 'f***'
mask('_____','dog');   // '__dog'

继承塞缪尔的想法，在上面这里。记住一个旧的SQL脚本，我尝试了这个:

a=1234;
'0000'.slice(a.toString().length)+a;

它适用于我能想到的所有情况:

a=     1 result  0001
a=    12 result  0012
a=   123 result  0123
a=  1234 result  1234
a= 12345 result 12345
a=  '12' result  0012

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); 
    }
}

http://www.webtoolkit.info/javascript_pad.html

/**
*
*  JavaScript string pad
*  http://www.webtoolkit.info/
*
**/

var STR_PAD_LEFT = 1;
var STR_PAD_RIGHT = 2;
var STR_PAD_BOTH = 3;

function pad(str, len, pad, dir) {

    if (typeof(len) == "undefined") { var len = 0; }
    if (typeof(pad) == "undefined") { var pad = ' '; }
    if (typeof(dir) == "undefined") { var dir = STR_PAD_RIGHT; }

    if (len + 1 >= str.length) {

        switch (dir){

            case STR_PAD_LEFT:
                str = Array(len + 1 - str.length).join(pad) + str;
            break;

            case STR_PAD_BOTH:
                var padlen = len - str.length;
                var right = Math.ceil( padlen / 2 );
                var left = padlen - right;
                str = Array(left+1).join(pad) + str + Array(right+1).join(pad);
            break;

            default:
                str = str + Array(len + 1 - str.length).join(pad);
            break;

        } // switch

    }

    return str;
}

可读性更强。

这两种解决方案的关键技巧是创建具有给定大小(比所需长度大一个)的数组实例，然后立即调用join()方法来生成字符串。join()方法被传递填充字符串(可能是空格)。由于数组是空的，在将数组连接到一个结果字符串的过程中，空单元格将被呈现为空字符串，只有填充将保留。这是一个很好的技巧。