This pointer JavaScript reference (complex)

mmetzger
mmetzger used Ask the Experts™
on
Experts,

I am making a generic trim function for JavaScript and extending this trim function the String object in JavaScript.

I have two functions that do the trim.  rtrim and ltrim.  As the names imply they trim the right and left sides of the string.  However, since I am extending this function to the JavaScript String object I am using the this pointer to pass information between the two functions.  But, it does not appear to work.

--Code Begin---
String.prototype.trim=function()
{
   var trimedStr = this.rtrim(this.ltrim());
   return trimedStr;
}  

String.prototype.ltrim=function()
{
  var trimChars = new Array(9,10,13,32);
  var trimStrLen = this.length;
  var startidx = 0;
  var trimedStr = "";
 
  for (var i=0;i<trimStrLen;i++)
  {      
    if (this.charCodeAt(i) != trimChars[0] && this.charCodeAt(i) != trimChars[1] &&
        this.charCodeAt(i) != trimChars[2] && this.charCodeAt(i) != trimChars[3])
    {
      startidx = i;
      break;
    }
  }  
 
  return this.substring(startidx,trimStrLen);
}

String.prototype.rtrim=function()
{
  var trimChars = new Array(9,10,13,32);
  var trimStrLen = this.length-1;
  var startidx = trimStrLen;
  var trimedStr = "";
 
  for (var i=trimStrLen;i>0;i--)
  {  
     if (this.charCodeAt(i) != trimChars[0] && this.charCodeAt(i) != trimChars[1] &&
        this.charCodeAt(i) != trimChars[2] && this.charCodeAt(i) != trimChars[3])
    {
      startidx = i;
      break;
    }  
  }  
   
  return this.substring(0,startidx+1);
}

var mytestvar = " -teststring- ";
var trimstr;

alert(mytestvar.length);
trimstr = mytestvar.trim();
alert(trimstr.length);
--Code End--

If I change the (trimstr = mytestvar.trim();) to (trimstr = mytestvar.rtrim(); or trimstr = mytestvar.ltrim();) then the string comes back trimed. But, not when I use the main function that is supposed to call both routines.

Any ideas?
-mmetzger
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Commented:
Solution was found on my own.

<b>Please refund my points EE.</b>

Solution as follows: posted by mmetzger

function trim(trimStr)
{    
   var trimedStr = rtrim(ltrim(trimStr));
   return trimedStr;
}  

function ltrim(trimStr)
{
  var trimStrLen = trimStr.length;
   
  for (var i=0;i<trimStrLen;i++)
  {
    var aCharCode = trimStr.charCodeAt(i);
   
    if (isWhiteSpace(aCharCode) == false)
    {
       break;
    }
  }  
 
  return trimStr.substring(i,trimStrLen);
}

function rtrim(trimStr)
{
  var trimStrLen = trimStr.length-1;
   
  for (var i=trimStrLen;i>0;i--)
  {
    var aCharCode = trimStr.charCodeAt(i);
   
    if (isWhiteSpace(aCharCode) == false)
    {
      break;
    }      
  }  
 
  return trimStr.substring(0,i+1);
}

function isWhiteSpace(possWsChar)
{
  /* White space chars
  9  = TAB
  10 = LF (line feed)
  12 = FF (form feed)
  13 = CR (Carriage return)
  32 = Space */

  var trimChars = new Array(9,10,12,13,32);
  var WsFound = false;
   
  for (var i=0;i<trimChars.length;i++)
  {    
    if (possWsChar == trimChars[i])
    {
      WsFound = true;
    }
  }
 
  return WsFound;  
}
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