Here is a handy collection of JavaScript prototypes compiled by James Haley, I personally found these quite useful and thus I am sharing them. These are pretty much self explanatory snippets and perform some regular tasks.

Array Remove – By John Resig (MIT Licensed)

Array.prototype.remove = function(from, to) {
    var rest = this.slice((to || from) + 1 || this.length);
    this.length = from < 0 ? this.length + from : from;
    return this.push.apply(this, rest);
};

Trim spaces

String.prototype.trim = String.prototype.trim || function() { return this.replace(/^\s+|\s+$/,""); }

Remove last full stop prototype

String.prototype.trimFullStops = function() { return this.replace(/^\.+|\.+$/,""); }

New line remove prototype

String.prototype.replaceNewLine = function() { return this.replace(/(\r\n|\r|\n)/g, ""); }

Replace breaks remove prototype

String.prototype.replaceBreaks = function() { return this.replace(/<br \/>|<br\/>/g, "\n"); }

String Trim to length or first Stop(.)

String.prototype.short = function(nLen) {
  var nFSPos = this.indexOf('.');
  return (this.length > nLen) ? ((nFSPos > -1) && (nFSPos < nLen + 1) && (nFSPos > 3)) ? this.split('.')[0].trim() + '…' : this.substring(0, nLen).trim() + '…' : this;
};

Encode for URL transport

String.prototype.encode = function() { return (this.length>0)?encodeURIComponent(this):this; };

Replace JS quotes

String.prototype.replaceQuotes = function() { return this.replace(/"/g,"\\\""); }

HTML remove tags prototype

String.prototype.stripTags = function() { return this.replace(/<\S[^>]*>/g, ""); }

Fix Numeric

String.prototype.tidyNumeric = function() { return Math.abs(this.replace(/[^0-9.]/ig,'').trimFullStops()); };

Tidy Decimal

Number.prototype.tidyDecimal = function(n) { return Math.abs(this.toFixed(n)); }

Convert to EM (base size 12px)

Number.prototype.toEm = function() { return (this/12).tidyDecimal(3); }

Right and Left cut

String.prototype.left = function(n) { return this.substr(0,n); }; String.prototype.right = function(n) { return this.substr((this.length-n),this.length); };

Convert date object into friendly string

Date.prototype.toClean = function() {
   if (this !== null) {
       var vDay = ((this.getDate()) < 10) ? '0' + (this.getDate()) : (this.getDate()),
           oMonths = ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec'],
           vMonth = oMonths[this.getMonth()],
           vYear = this.getFullYear().toString().right(2);
       return vDay + ' ' + vMonth + ' \'' + vYear;
   } else {
       return '[Invalid Date]';
   }

}

Convert date object into SQL supported

Date.prototype.toSQL = function() {
    var vDay = ((this.getDate()) < 10) ? '0' + (this.getDate()) : (this.getDate()),
        nMonth = (this.getMonth() + 1),
        vMonth = (nMonth < 10) ? '0' + nMonth : nMonth,
        vYear = this.getFullYear().toString(),
        vHours = ((this.getHours()) < 10) ? '0' + (this.getHours()) : (this.getHours()),
        vMinutes = ((this.getMinutes()) < 10) ? '0' + (this.getMinutes()) : (this.getMinutes()),
        vSeconds = ((this.getSeconds()) < 10) ? '0' + (this.getSeconds()) : (this.getSeconds());
    return vDay + '/' + vMonth + '/' + vYear + ' ' + vHours + ':' + vMinutes + ':' + vSeconds;
}

Remove all punctuation

String.prototype.clearPunc=function(){ return this.replace(/[\.,-\/#!$%\^&\*;:{}=\-_`~()]/g,"").replace(/\s{2,}/g," "); }

Highlight words by passed in value

String.prototype.highlight = function(vWords) {
    var oWords = vWords.clearPunc().stripTags().split(' '),
        vNewPhrase = this;
    oWords.each(function(o) {
        vNewPhrase = vNewPhrase.replace(new RegExp("(" + o + ")", "ig"), '<span class="highlight">$1</span>');
    });
    return vNewPhrase;
}