convert '1' to '0001' in JavaScrip

问题:

Possible Duplicate:
Is there a JavaScript function that can pad a string to get to a determined length?

How can I convert convert \'1\' to \'0001\' in JavaScript without using any 3rd party libraries. I have done this in php using spritf: $time = sprintf(\'%04.0f\',$time_arr[$i]);

回答1:

This is a clever little trick (that I think I\'ve seen on SO before):

var str = \"\" + 1
var pad = \"0000\"
var ans = pad.substring(0, pad.length - str.length) + str

JavaScript is more forgiving than some languages if the second argument to substring is negative so it will \"overflow correctly\" (or incorrectly depending on how it\'s viewed):

That is, with the above:

• 1 -> \"0001\"
• 12345 -> \"12345\"

Supporting negative numbers is left as an exercise ;-)

Happy coding.

回答2:

Just to demonstrate the flexibility of javascript: you can use a oneliner for this

function padLeft(nr, n, str){
    return Array(n-String(nr).length+1).join(str||\'0\')+nr;
}
//or as a Number prototype method:
Number.prototype.padLeft = function (n,str){
    return Array(n-String(this).length+1).join(str||\'0\')+this;
}
//examples
console.log(padLeft(23,5));       //=> \'00023\'
console.log((23).padLeft(5));     //=> \'00023\'
console.log((23).padLeft(5,\' \')); //=> \'   23\'
console.log(padLeft(23,5,\'>>\'));  //=> \'>>>>>>23\'

If you want to use this for negative numbers also:

Number.prototype.padLeft = function (n,str) {
    return (this < 0 ? \'-\' : \'\') + 
            Array(n-String(Math.abs(this)).length+1)
             .join(str||\'0\') + 
           (Math.abs(this));
}
console.log((-23).padLeft(5));     //=> \'-00023\'

Alternative if you don\'t want to use Array:

number.prototype.padLeft = function (len,chr) {
 var self = Math.abs(this)+\'\';
 return (this<0 && \'-\' || \'\')+
         (String(Math.pow( 10, (len || 2)-self.length))
           .slice(1).replace(/0/g,chr||\'0\') + self);
}

回答3:

String.prototype.padZero= function(len, c){
    var s= this, c= c || \'0\';
    while(s.length< len) s= c+ s;
    return s;
}

dispite the name, you can left-pad with any character, including a space. I never had a use for right side padding, but that would be easy enough.

回答4:

I use the following object:

function Padder(len, pad) {
  if (len === undefined) {
    len = 1;
  } else if (pad === undefined) {
    pad = \'0\';
  }

  var pads = \'\';
  while (pads.length < len) {
    pads += pad;
  }

  this.pad = function (what) {
    var s = what.toString();
    return pads.substring(0, pads.length - s.length) + s;
  };
}

With it you can easily define different \"paddings\":

var zero4 = new Padder(4);
zero4.pad(12); // \"0012\"
zero4.pad(12345); // \"12345\"
zero4.pad(\"xx\"); // \"00xx\"
var x3 = new Padder(3, \"x\");
x3.pad(12); // \"x12\"