What are useful JavaScript methods that extends built-in objects?

Question

What are your most useful, most practical methods that extends built-in JavaScript objects like String, Array, Date, Boolean, Math, etc.?

String

• format
• trim
• padding
• replaceAll & replaceAll

Array

• indexOf

Date

• toMidnight

Note : Please post one extended method per answer.

Answer 1

Use the prototype chain like this:

String.prototype.AddWorld = function() { return this+'World' }

"Hello ".AddWorld(); // returns the string "Hello World"

Answer 2

String Padding :

String.prototype.padLeft = function (length, character) { 
     return new Array(length - this.length + 1).join(character || ' ') + this; 
}
'trial'.padLeft(7, 'X'); // output : 'XXtrial'
'trial'.padLeft(7);      // output : '  trial'



String.prototype.padRight = function (length, character) { 
     return this + new Array(length - this.length + 1).join(character || ' '); 
}
'trial'.padRight(7, 'X'); // output : 'trialXX'
'trial'.padRight(7);      // output : 'trial  '

Answer 3

Array.prototype.indexOf = Array.prototype.indexOf || function (item) {
    for (var i=0; i < this.length; i++) {
        if(this[i] === item) return i;
    }
    return -1;
};

Usage:

var list = ["my", "array", "contents"];
alert(list.indexOf("contents"));     // outputs 2

Answer 4

String Replace All :

String.prototype.replaceAll = function(search, replace)
{
    //if replace is null, return original string otherwise it will
    //replace search string with 'undefined'.
    if(!replace) 
        return this;

    return this.replace(new RegExp('[' + search + ']', 'g'), replace);
}

var str = 'ABCADRAE';
alert(str.replaceAll('A','X')); // output : XBCXDRXE

Answer 5

Date.toMidnight

Date.prototype.toMidnight = function(){ 
  this.setMinutes(0); 
  this.setSeconds(0); 
  this.setHours(0) 
}

Answer 6

// left trim
String.prototype.ltrim = function () {
    return this.replace(/^\s+/, '');
}

// right trim
String.prototype.rtrim = function () {
    return this.replace(/\s+$/, '');
}

// left and right trim
String.prototype.trim = function () {
    return this.ltrim().rtrim();
}

Answer 7

There are a ton of String.prototype functions from James Padolsey

http://github.com/jamespadolsey/string/tree/master

These include:

• camelize
• contains
• count
• enclose
• extract
• forEach
• forEachWord
• linkify
• many
• randomize
• remove
• reverse
• shorten
• sort
• toDOM
• trim
• wrap

Answer 8

String.format

String.prototype.format = function(values)
{
    var regex = /\{([\w-]+)(?:\:([\w\.]*)(?:\((.*?)?\))?)?\}/g;

    var getValue = function(key)
                   {
                        if(values == null || typeof values === 'undefined')
                            return null;

                        var value = values[key];
                        var type = typeof value;

                        return type === 'string' || type === 'number' ? value : null;
                   };

    return this.replace(regex, function(match) 
                                { 
                                    //match will look like {sample-match}
                                    //key will be 'sample-match';
                                    var key = match.substr(1, match.length - 2);

                                    var value = getValue(key);

                                    return value != null ? value : match;
                                });
};

Usage:

alert('Program: {key1} {key2}'.format({ 'key1' : 'Hello', 'key2' : 'World' })); //alerts Program: hello world

Answer 9

Array contains:

Array.prototype.contains = function(obj) {
    for (var i=0; i < this.length; i++) {
        if(this[i] === obj) return i;
    }
    return -1;
}

Usage:

var arr = [1, 2, 3];
alert(arr.contains(2));

This little helper function tells you if your array contains an object. If it does then the index of the object is returned, otherwise -1 is returned.

Free Friday afternoon tip: don't ever ever ever modify the Object prototype. That would be just asking for a whole world of pain - I learnt this the hard way :)

Answer 10

The various list manipulation prototypes are always great. Since you want only one per post, I'll just post foldl, which I discovered via SML (it "folds" the list, left to right, it has a counter part in foldr of course).

Array.prototype.foldl = function(fnc,start) {
    var a = start;
    for (var i = 0; i < this.length; i++) {
        a = fnc(this[i],a);
    }
    return a;
}

Some trivial examples could be:

var l = ["hello" , "world"];
l.foldl(function(i, acc) { return acc+" "+i; }, "") // => returns "hello world"

Sadly, the failure of standard DOM methods to return true arrays makes alot of these such methods rather useless. And if you're using a Lib of some sort, they often define methods like these already (map, filter, exists, etc).

Answer 11

Here's the nice extension for the Date object that allows you to format the date very easily. It uses PHP's date syntax so those familiar with PHP will get it in no time. Others have a huge list of possible switches on the site as well. Personally I haven't found easier way to format dates to various formats.

Date Format

Answer 12

Here's another implementation of String.replaceAll() method

String.prototype.replaceAll = function(search, replace) {
    if (replace === undefined) {
        return this.toString();
    }
    return this.split(search).join(replace);
}

The difference between this one and solution posted here is that this implementation handles correctly regexp special characters in strings as well as allows for word matching

Answer 13

PHP.JS is a very nice effort to port most of PHP's functions to JavaScript. They currently have an extremely impressive list:

Online at: http://phpjs.org/functions/index

Answer 14

A collection of functions I use a lot can be found here:

http://svn.asplib.org/asplib1.2/core/string.asp

http://docs.hyperweb.no/objects/String/

Answer 15

I have used the Array.Map function outlined by Scott Koon a couple of times.

http://www.lazycoder.com/weblog/2009/08/12/a-simple-map-function-for-plain-javascript-arrays/

Array.prototype.map = function(fn) {
    var r = [];
    var l = this.length;
    for(i=0;i<l;i++)
    {
        r.push(fn(this[i]));
    }
    return r; 
};

Answer 16

// This replaces all instances of 'from' to 'to' even when
// 'from' and 'to' are similar (i.e .replaceAll('a', 'a '))
String.prototype.replaceAll = function(from, to) {
    var k = this;
    var i = 0;
    var j = from.length;
    var l = to.length;

    while (i <= k.length)
        if (k.substring(i, i + j) == from) {
        k = k.substring(0, i) + k.substring(i).replace(from, to);
        i += l;
    }
    else
        i++;

    return k;
};

Answer 17

Function.prototype.bind from the Prototype library.

Similar to call and apply but allows you to return a reference to a function that is called in a particular context instead of executing it immediately. Also allows you to curry parameters. It's so useful that it became a part of ECMAScript 5 and is already being implemented natively in browsers.

Function.prototype.bind = function() {
  var __method = this, args = Array.prototype.slice.call(arguments), object = args.shift();
  return function() {
    var local_args = args.concat(Array.prototype.slice.call(arguments));
    if (this !== window) local_args.push(this);
    return __method.apply(object, local_args);
  }
}

Answer 18

These two are wrappers for inserting and deleting elements from a particular position in an Array because I don't like the name splice.

// insert element at index
Array.prototype.insertAt = function(element, index) {
    this.splice(index, 0, element);
}

// delete element from index
Array.prototype.removeAt = function(index) {
    this.splice(index, 1);
}

Some more useful Array methods to get away from using indexes:

Array.prototype.first = function() {
    return this[0] || undefined;
};

Array.prototype.last = function() {
    if(this.length > 0) {
        return this[this.length - 1];
    }
    return undefined;
};

Array.prototype.max = function(array){
    return Math.max.apply(Math, array);
};

Array.prototype.min = function(array){
    return Math.min.apply(Math, array);
};

Some useful functions from the MooTools library:

Function.delay

Used to execute a function after the given milliseconds have elapsed.

// alerts "hello" after 2 seconds.
(function() {
    alert("hello");
}).delay(2000);    ​

Number.times

Similar to Ruby's times method for numbers, this accepts a function and executes it N times where N is the numbers value.

// logs hello 5 times
(5).times(function() {
    console.log("hello");
});

Answer 19

There is a nice article at http://maiaco.com/articles/js/missingArrayFunctions.php describing six helpful functions to add to the Array prototype. The functions are linearSearch (same as indexOf given in another answer), binarySearch, retainAll, removeAll, unique, and addAll. The article also includes the JavaScript code for each of the six functions and example code showing how to use them.