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Re: Parsing String of Named Function & Converting To Source

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Seni Seven <OneWhoLovesYou@humanitarian.ca.invalid> writes:

> Suppose I have HTML markup with a SCRIPT element as shown below:
>
>   <script type="text/javascript">
>   function multiply(a, b) {
>      return a * b;
>   }
>   var i = multiply(2, 5);
>   document.write("The value of <i>i</i> is " + i);

Invalid HTML 4 markup. You should escape the </ inside the string.

>   </script>
>
> All of this markup and contained script code is retrieved as a string using 
> Ajax.

So, it's a string with the above content (newlines and all).

> I have an HTML parser with support for parsing the string containing the 
> script code.

Ok.

> In parsing the contained code (using JavaScript, of course), how would you 
> convert the contained script code from string into source?

What's the difference? I assume your HTML parser extracts the content
of the script element as a string.
What do you want to do with that string?

> What I have found so far (using Firebug in Firefox for development) is this:
>
> 1) Isolating the string "function multiply(a, b) { return a * b; }" and then 
> passing that string as an argument to eval() does not cause the definition 
> of the function named "multiply," it seems.

It probably does, but in the scope where the eval is executed, not at
the global scope.
For that, you can use, e.g., 
  window.eval(sourceString);
(or any other non-direct call to eval).


> 2) I can parse the function definition in a way to create the string:
>
>   "var multiply = new Function (\"a\", \"b\", \"{ return a * b; }\");"

How wasteful :) The function syntax is perfectly fine, no need to make
it more convoluted.

> and then use eval() on it (without error).  And then when I eval() the 
> global level code in a debugger (Firebug in FireFox), as so
>
>    eval("var i = multiply(2, 5); document.write(\"The value " +
>      "of <i>i</i> is \" + i);");  // parsed code as string on one line
>
>
> the value of identifier 'i' is immediately set to 10 in the debugger, but 
> the debugger exits with error 'multiply is not defined', which indicates 
> multiple levels of execution contexts, I suppose.  In fact, if I just do an 
> eval() on the "multiply" assignment of the Function constructor, the 
> identifier 'multiply' is still not defined.
>
> QUESTION:  What's the solution to the goal I want to achieve?

Try:
  var script = document.createElement("script");
  script.textContent = sourceString;
  document.body.appendChild(script);
This executes the code as top-level, non-eval code (which there is no way
to do in pure Javascript).
No guarantees wrt. old browsers, but it seems to work in the current versions.

Alternatively, just use a non-direct call to eval.
 var topLevelEval = eval;
 topLevelEval(sourceString);

> The string representing the markup obtained by Ajax retrieval is then passed 
> to a parsing function which is supposed to do it all:  parses the HTML 
> markup using DOM methods to insert the DocumentFragment into the main 
> document tree.  It also parses CSS (stylesheets and style attributes), as 
> well as any Javascript contained inside SCRIPT elements.  Everything becomes 
> part of the interactive document by using DOM method calls, HTML --> element  
Why not pass it as something easier to parse and separate into
CSS/HTML/JS, e.g., JSON?

/L
-- 
Lasse Reichstein Holst Nielsen
 'Javascript frameworks is a disruptive technology'
  

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Thread

Parsing String of Named Function & Converting To Source Seni Seven <OneWhoLovesYou@humanitarian.ca.invalid> - 2011-10-18 13:48 +0000
  Re: Parsing String of Named Function & Converting To Source Andreas Bergmaier <andber93@web.de> - 2011-10-18 16:03 +0200
    Re: Parsing String of Named Function & Converting To Source Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-10-18 19:29 +0200
  Re: Parsing String of Named Function & Converting To Source Lasse Reichstein Nielsen <lrn.unread@gmail.com> - 2011-10-18 18:34 +0200
    Re: Parsing String of Named Function & Converting To Source Seni Seven <OneWhoLovesYou@humanitarian.ca.invalid> - 2011-10-19 08:01 +0000
    Re: Parsing String of Named Function & Converting To Source Dr J R Stockton <reply1142@merlyn.demon.co.uk> - 2011-10-19 20:09 +0100

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