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JavaScript

Posted by John Grillo
John Grillo
30,241 Points

How to pad numbers with 0's?

Howdy all, I'm making a decimal to hexadecimal converter and I'm having a hard time padding the results with zero's. For example, when I convert 10 is A,

it should read:

10 is 00A.

Does anyone have any advice on how to do this? I'd be happy to post my code if it would be helpful.

PS My easy integer||decimal to hexadecimal value is: yourNumber.toString(16);

John Grillo
John Grillo
30,241 Points

This was the method I ultimatly used, hopefully others find it helpful. It can be appended to any call as .zeropad() ;

String.prototype.zeropad = function() 
{
 return ("000" + this).slice(-3);  // the negative number starts at the end of the string and moves leftwards. 

 //("00000" + hexString).slice(-5); //  if using n=123 returns 00123,
 //("     " + hexString).slice(-5); // if you use n=123, returns "  123" (with two spaces).
}

The best part is that it works with just about anything (as shown above) and JavaScript is much, much nicer about typecasting and data conversion than C++ ever was or will be.

3 Answers

John Grillo
John Grillo
30,241 Points

Dear mods, both are good, but I think I found a simpler method for what I was trying to accomplish.

String.prototype.zeropad = function() 
{
 return ("000" + this).slice(-3);  // the negative number starts at the end of the string and moves leftwards. 

 //("00000" + hexString).slice(-5); //  if using n=123 returns 00123,
 //("     " + hexString).slice(-5); // if you use n=123, returns "  123" (with two spaces).
}

it gets called as .zeropad to the end of the string/call. it adds the exact amount of zeros needed and by using the 000, then cut it appropriately. Your solutions are fairly clever though. Have an upvote.

Roberto Alicata
Roberto Alicata
Courses Plus Student 39,959 Points

This is a good start point, but I suggest to add some parameter to make this function more usable, at least add the number of the zeros you need in return string.

String.prototype.zeropad = function(format) 
{
 str = Array(format).join("0");
 return (str + this).slice(-format);
};
Hugo Paz
Hugo Paz
15,622 Points
Hugo Paz
Hugo Paz
15,622 Points

Hi John,

Could something like this work for you?

//for testing purposes only, use the result of the conversion here
var result = 'A';

var length = result.length;

var zeros = '0';

var additional = '';
//this will only check if the final result is smaller than 3 characters, change the value accordingly
for(var i = length; i < 3; i++){
    additional = additional.concat(zeros); 
}

var finalValue = additional.concat(result);
John Grillo
John Grillo
30,241 Points

Yes, that certainly is helpful but not what I went with. see my comment below. Have an upvote anyway!

Roberto Alicata
PLUS
Roberto Alicata
Courses Plus Student 39,959 Points
Roberto Alicata
Roberto Alicata
Courses Plus Student 39,959 Points

If you need to use this conversion very often you can choose to implement a formatter:

Number.prototype.formatHEX = function(format) {
  if ((typeof format !== "string")) {return '';} 
  that = this.toString(16);
  formatLength = format.length;
  numberLength = that.length;

  var num = '';

  for(var i = 0; i < (formatLength - numberLength); i++){
    num = num.concat('0'); 
  }
  return num + that;
};

var a = 42;
console.log(a.formatHEX('00000'));  // => "0002a"