Javascript - creating a new Array method

Question

I would like to extend the Javascript built-in Array object by addind a new method: searchByRegexp

Basically the method will get a regexp as input and will return:
_ a string representing the element of the array that matches the regexp (if more than one match, the first one will be returned)
_ an empty string if none of the elements matches the regular expression.

• Lepidosteus: What is blocking you ? Adding a function to the prototype, doing that specific function ... ? What have you tried ?
• clockworkgeek: Just for interest or maybe convenience there are libraries which already do this. See Enumerable.grep for example.

Answer 1

Quick and dirty (fiddle for your fiddling pleasure):

Array.prototype.searchByRegexp = function (rx) {
 for(var i = 0, ln = this.length; i < ln; i++) {
 // test item i
 if(rx.test(this[i])) {
 return this[i] + "";
 }
 }
 // return an empty string if no matches are found
 return "";
}

However, you may wish to implement more general methods instead...

Array.prototype.find = function(delegate) { 
 for(var i = 0, ln = this.length; i < ln; i++) {
 if(delegate(this[i])){
 return this[i]; 
 }
 }
 return null;
}
Array.prototype.findAll = function(delegate) { 
 var results = [];
 for(var i = 0, ln = this.length; i < ln; i++) {
 if(delegate(this[i])){
 results.push(this[i]); 
 }
 }
 return results ;
}
Array.prototype.each = function (delegate) {
 for (var i = 0, ln = this.length; i < ln; i++) {
 delegate(this[i], i);
 }
}

... which could then perform regex comparison like so:

// test values
var sizes = ["Small", "Medium", "Large", "Extra-Large", "Extra-Extra-Large"];
// Print single value or blank
document.write(sizes.find(function(size){
 return /large/i.test(size);
}) || ""); 
// horizontal rule to separate our results
document.write("<hr/>");
// Print all matches
sizes.findAll(function(size){
 return /large/i.test(size);
}).each(function(size){
 document.write(size + "<br/>"); 
}); 

• Dan: Great answer, thanks. I would like to put all those extra functions in a file. Is there a convension for its name? I mean, for a file extending the prototype of a built-in javascript object.
• canon: I'm not aware of any file-naming conventions for prototype extensions.

Answer 2

As of today, using Google Chrome, the provided solution breaks the iteration over the array.

After Array.prototype.searchByRegexp = function ..., if you iterate with for (var k in arrayInstance), the value searchByRegexp will be in the keys, not only the real array keys.

To prevent that you should use Object.defineProperty(Array.prototype, ...

Object.defineProperty(Array.prototype, 'searchByRegexp', {
 value: function (rx) {
 for(var i = 0, ln = this.length; i < ln; i++) {
 // test item i
 if(rx.test(this[i])) {
 return this[i] + "";
 }
 }
 // return an empty string if no matches are found
 return "";
 },
 enumerable: false
});