Category: Tips

Multiple replacements with JavaScript Regular Expressions

Jayesh WadhwaniLeave a comment

Recently I came across a piece of code using the replace command. Looking at the code I got the feeling that the author was not very comfortable with Regex replacements. Here is the snippet which I have modified slightly to explain my point.

<!DOCTYPE html>
<html>
<head>
<script src="jquery-1.4.2.js"></script>
<script language = "JavaScript" type = "text/javascript">

  $(document).ready(function (){
      
      var text = [];
      text.push('Suddenly, the wolf appeared beside her. "What are you doing out here, little girl?"\n');
      text.push('the wolf asked in a voice as friendly as he could muster.\n');
      text.push('I\'m on my way to see my Grandma who lives through the forest, near the brook,"  Little Red Riding Hood replied.');
      
      var postdata = [];   
      var re = new RegExp("\n");
      var re1 = new RegExp("[.]", "g");
      var re2 = new RegExp("[,]", "g");
      var re3 = new RegExp("[?]", "g");
      var re4 = new RegExp("[!]", "g");
      var re5 = new RegExp("[:]", "g");
      var re6 = new RegExp("[;]", "g");
      var re7 = new RegExp("[']", "g");
      var re8 = new RegExp('["]', "g");

      $.each(text, function(){
         var content = this.replace(re, ' ');
         content = content.replace(re1, '').replace(re2, '').replace(re3, '').replace(re4, '')
            .replace(re5, '').replace(re6, '').replace(re7, '').replace(re8, '');
         
         postdata.push(content);
      });

      //print it out
      for(var i in postdata){
         console.log('OLD: ' + postdata[i]);
      }
            
  });
</script>
</head>
<body>
<!-- some stuff -->
</body>
</html>

As is obvious all the above code does is replaces the character ‘\n’ with a space and characters dot, comma, question mark, exclamation, colon, semi-colon, single and double quotes with an empty string.

If you were to run this the output would be:
Console [7]=
OLD: Suddenly the wolf appeared beside her What are you doing out here little girl

Console [8]=
OLD: the wolf asked in a voice as friendly as he could muster

Console [9]=
OLD: Im on my way to see my Grandma who lives through the forest near the brook Little Red Riding Hood replied

Fortunately JavaScript’s Regex engine is quite robust and flexible and can pretty much take on any other Regex engines. So the above code can be written as follows:

<!DOCTYPE html>
<html>
<head>
<script src="jquery-1.4.2.js"></script>
<script language = "JavaScript" type = "text/javascript">

  $(document).ready(function (){
      
      var text = [];
      text.push('Suddenly, the wolf appeared beside her. "What are you doing out here, little girl?"\n');
      text.push('the wolf asked in a voice as friendly as he could muster.\n');
      text.push('I\'m on my way to see my Grandma who lives through the forest, near the brook,"  Little Red Riding Hood replied.');

      var postdata = [];
      var re = /['\n']/g;
      var re1 = /[\.\,\?\!\:\;\'\"\']/g;
      
      for(var i in text){
         var content = text[i].replace(re, ' ').replace(re1, '');
         postdata.push(content);
      };

       for(var i in postdata){
         console.log('NEW: ' + postdata[i]);
      }
      
  });
</script>
</head>
<body>
<!-- some stuff -->
</body>
</html>

The output is:

Console [10]=
NEW: Suddenly the wolf appeared beside her What are you doing out here little girl

Console [11]=
NEW: the wolf asked in a voice as friendly as he could muster

Console [12]=
NEW: I m on my way to see my Grandma who lives through the forest near the brook Little Red Riding Hood replied

As you can see it is much more elegant and many times faster. Also notice that instead of using the jQuery $.each iterator I have use the JavaScript for…in. This is much faster than $.each. I recommend that you use this whenever possible.

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Why not call it event functions?

Jayesh WadhwaniLeave a comment

When working with JavaScript/jQuery intensive applications one always has to deal with a multitude of AJAX calls. AJAX calls like the name suggests are asynchronous. Though the asynchronous has its advantages about background processing it creates a little bit of a hurdle if you need to validate the return result before moving on.

Libraries like jQuery do allow you make the call synchronous but I am not a big fan of that. While the client-server communication marriage that we call AJAX has come a long way, any interruption in this relationship will make the client browser pay a heavy price in terms of timeouts and freezes.

To make code more manageable I do the following:

//my handlers
 var fnLockReleasedHandler = function(event, spec){
     alert('Lock status is: ' + spec.lockStatus);
 };
   
var fnReleaseLockHandler = function(event, spec){
    $.get('/xxx/controller/releaseLock', {userId: spec.userId}, function(data){
         $(document).trigger('lockReleased.am', [{lockStatus: data}]);
    });
};
   
//bindings
   $(document).bind({
      'lockReleased.am': fnLockReleasedHandler,
      'releaseLock.am': fnReleaseLockHandler
   });

I have used ‘document’ as an example. I always prefer to bind my custom events to a high level root element. Also note that I have name-spaced my events. Good practice to follow, this way my events remain only my events.

To trigger this I can use something simple as:

$(document).trigger('releaseLock.am', [{userId: 1234}]);

This trigger calls the ‘fnReleaseLockHandler’ and that contains an AJAX call. The result of the call triggers the ‘fnLockReleasedHandler’ which brings with itself the return results.

I usually like to have an object of such custom events and their respective handlers neatly encapsulated using closures to use application wide.

All this but I have no name for it!