JavaScript array_pad

Returns a copy of input array padded with pad_value to size pad_size

function array_pad ( input, pad_size, pad_value ) {
    // Returns a copy of input array padded with pad_value to size pad_size  
    // 
    // version: 1008.1718
    // discuss at: http://phpjs.org/functions/array_pad    // +   original by: Waldo Malqui Silva
    // *     example 1: array_pad([ 7, 8, 9 ], 2, 'a');
    // *     returns 1: [ 7, 8, 9]
    // *     example 2: array_pad([ 7, 8, 9 ], 5, 'a');
    // *     returns 2: [ 7, 8, 9, 'a', 'a']    // *     example 3: array_pad([ 7, 8, 9 ], 5, 2);
    // *     returns 3: [ 7, 8, 9, 2, 2]
    // *     example 4: array_pad([ 7, 8, 9 ], -5, 'a');
    // *     returns 4: [ 'a', 'a', 7, 8, 9 ]
    var pad = [], newArray = [], newLength, i=0; 
    if ( input instanceof Array && !isNaN( pad_size ) ) {
        newLength = ( ( pad_size < 0 ) ? ( pad_size * -1 ) : pad_size );
        if ( newLength > input.length ) {
            for ( i = 0; i < ( newLength - input.length ); i++ ) { newArray [ i ] = pad_value; }            pad = ( ( pad_size < 0 ) ? newArray.concat( input ) : input.concat( newArray ) );
        } else {
            pad = input;
        }
    } 
    return pad;
}

external links: original PHP docs | raw js source

Examples

» Example 1

Running

1	array_pad([ 7, 8, 9 ], 2, 'a');

Should return

1	[ 7, 8, 9]

» Example 2

Running

1	array_pad([ 7, 8, 9 ], 5, 'a');

Should return

1	[ 7, 8, 9, 'a', 'a']

Dependencies

No dependencies, you can use this function standalone.

Open syntax issues

php.js uses JsLint to help us keep our code consistent and prevent some common bugs.

Eventually we want all code to pass or at least take into consideration most fixes suggested by JsLint, following this JsLint configuration we’ve decided on.

Authors

Thanks to the following developers, you get to have array_pad goodness in JavaScript.

Waldo Malqui Silva ( original )

Comments

Add Comment

Name

Website

Title

Content

Use:

[CODE]
your_stuff('here');
[/CODE]

for proper code formatting
By submitting code here you are allowing us to use it in php.js hence dual licensing it under the MIT and GPL licenses

Rafał Kukawski
Jul 5th

Nothing special, but this is my approach to this function

function array_pad(input, pad_size, pad_value){
    try {
        pad_size |= 0; // force pad_size to be int
        var diff = Math.abs(pad_size) - input.length,
            pad = [];

        if(diff <= 0){
            return input.slice(0);
        }

        while(diff--){
            pad.push(pad_value);
        }

       return pad_size < 0 ? pad.concat(input) : input.concat(pad);
    } catch(e) {
        return null; // PHP throws a warning and returns null when first param isn't an array
    }
}

I wrapped the functions body with try..catch, in case the input isn't an array or anything else that has concat and slice methods (the function works also with strings, cause both methods are included in String prototype :-P). To be 99.9% compatible with PHP and not let this function handle strings, just add a condition

if(!(input instanceOf Array)){
throw "Not an array";
}

if(!(input instanceOf Array)){
return null;
}

Some people prefer also "better" checking for arrays

Object.prototype.toString.call(input) !== '[object Array]'

Another problem is handling arrays with non-numeric indexes. I don't see a stable strategy along the whole phpjs project, that is why I didn't implement support for it.

Yury Ramanouski
Jul 2nd

// Even quicker function is possible!
Array.prototype.pad = function(pad_size, pad_value){
  var tail_length = Math.abs(pad_size) - this.length;
  if(tail_length <= 0){
    return this; // replace "this" with "this.slice(0)" if you want a copy
  }

  var tail = [];
  var subTail = [pad_value];
  for( ; ; ){
    if(tail_length % 2){
      tail = tail.concat(subTail);
    }
    if(tail_length >>= 1){
      subTail = subTail.concat(subTail);
    }
    else{
      break;
    }
  }

  return pad_size < 0 ? tail.concat(this) : this.concat(tail);
}