how to save a value from textarea to a blank file?

Question

I'm making a webpage wherein a user can make his/her own functions, then those functions will become like an option to the side of the webpage so when they are click/selected they can be used. Here's the flow

1. User creates function written in js
2. when save button is click it will automatically be save to Savedfunction.js file
3. the created function will be called as a checkbox so that it can be use

Here's a picture to further elaborate the problem:

Answer 1

First of all javascript can't save files on you computer (except you use ie). security,privacy...

---

If you want to let the user download his created file:

Chrome has the new download attribute but it works also on other brosers without the download attribute.

var txt='var x = 3,lol=fun;';

function dl(data,filename){
 var b=document.createElement('a');
 b.download=filename;
 b.textContent=filename;
 b.href='data:application/json;base64,'+
 window.btoa(unescape(encodeURIComponent(data)));
 return b
}

document.body.appendChild(dl(txt,'my.js'));

DEMO

http://jsfiddle.net/8yQcW/

in the comment is also a link for automatic download.

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Want to save the data on your server:

note:if you want to save the function to the server you need a server language like php

<?php
if($_POST['fn']&&$_POST['data']){
 $fh=fopen($_POST['fn'],'w') or die("can't open file");
 if(fwrite($fh,$_POST['data'])){
  echo '["ok":"file saved"]';// maybe return the saved code.
  //echo json_encode($_POST);
 }else{
  echo '["error":"can\'t save the file"]';
 }
 fclose($fh);
}
?>

---

Want to save the data only on the users computer (using modern web technologies?)

you can also store the data inside (clientSide):

window.localStorage
window.sessionStorage

webSQL

indexedDB

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Want to execute the script from it's string?

don't use eval();

use:

 var js="var x='hey';alert(x);"
 (new Function(js))()

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To achieve what you need you need to mix this technologies.

if you have any other questions just ask.