String.replace; replace by function result problem

Question

I have this piece of code:

var myObj = function () {
   this.complex = function (text) { /* long piece of code */ }
   this.parse(text) {
     return text.replace(/valid_pattern/gi, function ($1) { return this.complex($1); } );
   }
}

Of course calling this.complex($1) won't do the trick, because I'm in the scope of the anonymous function. I can't re-scope the anonymous function using .call(this) statement either, because in th ta case I would lose the parameters passed to the function by String.replace.

So far I'm using the concrete instance of the object. This is my solution:

var instance = new myObj;
var myObj = function () {
   this.complex = function (text) { /* long piece of code */ }
   this.parse(text) {
     return text.replace(/valid_pattern/gi, function ($1) { return instance.complex($1); } );
   }
}

So far it's sufficient to my needs, but I'm wondering if there is any universal solution to this problem. The only idea that has worked for me so far is this:

function ($1) { return (new myObj).complex($1); }

... which suffers from serious performance issues. Any ideas would be greatly appreciated.

-- D.

P. S. Sorry about my English, it's not my first language.

Your code makes no sense! Is 'parse' meant to be a function? — James
– James, Commented Jan 8, 2009 at 17:09

rkj · Accepted Answer · 2009-01-08 19:34:55Z

4

Maybe try:

var myObj = function () {
   this.complex = function (text) { /* long piece of code */ }
   this.parse(text) {
     var that = this;
     return text.replace(/valid_pattern/gi, function ($1) { return that.complex($1); } );
   }
}

It is one of the most useful tricks :-)

UPDATE: The trick is not mine, I learned it (as most of things I know about Javascript) from: Douglas Crockford

edited Jan 8, 2009 at 19:34

answered Jan 8, 2009 at 16:08

rkj

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1 Comment

Dero Over a year ago

This "that" sure solves the problem. :o) I try to avoid assistive variables wherever possible. But I understand from your answer, that this approach is considered as a "standard" solution for this kind of situations. Thanks!

meouw · Accepted Answer · 2009-01-08 17:17:01Z

2

This is what prototype and others do

// Monkey Patching, not everyone likes it
Function.prototype.bind = function( obj ) {
    var _this = this;
    return function() {
        return _this.apply( obj, arguments )
    }
}

Now you can do this

var myObj = function () {
   this.complex = function (text) { /* long piece of code */ }
   this.parse = function(text) {
     return text.replace(/valid_pattern/gi, function ($1) { return this.complex($1); }.bind( this ) );
   }
}

O = new myObj();
alert( O.parse( 'some text' );

answered Jan 8, 2009 at 17:17

meouw

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Comments

Jimmy · Accepted Answer · 2009-01-08 16:07:35Z

0

declare a variable for that.

var myObj = function () {
  var foo = this.complex = function (text) { /* long piece of code */ }
  this.parse(text) {
    return text.replace(/valid_pattern/gi, foo );
  }
}

answered Jan 8, 2009 at 16:07

Jimmy

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