I have an AJAX-based website using JavaScript on the client. Certain operations on the site cache large result sets from service calls in the browser (i.e. hundreds of megabytes). These are throw-away results. They will be viewed for a short time and then need to be cleared from memory.

I've written a small test site that loads a bunch of junk in memory and then calls JavaScript's delete method. This works great in Firefox (memory almost instantly gets returned). Internet Explorer 8 (haven't tried 7) doesn't free the memory until the page is refreshed or closed.

Does anyone know how to drop IE's memory usage using JavaScript/Ajax (no page refreshes)?

Below is my sample client code:

function load() {
 var x = ['dfjasdlfkjsa;dflkjsad;flkjsadf;lj'];

 for( var i = 0; i < 10000000; ++i ) {
  x.push('asdfasfasfsfasdfkasjfslafkjslfjsalfjsaldfkjasl;dfkjsadfl;kjsdflskajflskfjslakfjaslfkjsaldfkjsaldfksdfjk');
 }

 alert('deleting');   // <--- memory usage around 500mb
 delete x;            // <--- immediate results in Firefox 3.5 (not IE8)
 alert('done');
}

UPDATE: Setting the variable to 'null' does not immediately clear the memory (as that is left up to the garbage collector). Also, setting a variable null only gets a single reference where there might be multiple references.

I have an AJAX-based website using JavaScript on the client. Certain operations on the site cache large result sets from service calls in the browser (i.e. hundreds of megabytes). These are throw-away results. They will be viewed for a short time and then need to be cleared from memory.

I've written a small test site that loads a bunch of junk in memory and then calls JavaScript's delete method. This works great in Firefox (memory almost instantly gets returned). Internet Explorer 8 (haven't tried 7) doesn't free the memory until the page is refreshed or closed.

Does anyone know how to drop IE's memory usage using JavaScript/Ajax (no page refreshes)?

Below is my sample client code:

function load() {
 var x = ['dfjasdlfkjsa;dflkjsad;flkjsadf;lj'];

 for( var i = 0; i < 10000000; ++i ) {
  x.push('asdfasfasfsfasdfkasjfslafkjslfjsalfjsaldfkjasl;dfkjsadfl;kjsdflskajflskfjslakfjaslfkjsaldfkjsaldfksdfjk');
 }

 alert('deleting');   // <--- memory usage around 500mb
 delete x;            // <--- immediate results in Firefox 3.5 (not IE8)
 alert('done');
}

UPDATE: Setting the variable to 'null' does not immediately clear the memory (as that is left up to the garbage collector). Also, setting a variable null only gets a single reference where there might be multiple references.

• javascript
• ajax
• internet-explorer
• memory
• memory-management

5 Answers 5

IE (well, technically, JScript) has an undocumented CollectGarbage method, which supposedly forces garbage collector to run immediately. You might want to play with that, but from my experience, nulling references is enough most of the time.

Instead of using the delete method, set the variable to null. This seems to be the best way to clear up memory cross-browser (delete is notoriously flaky). It works the same as my other answer here.

alert('deleting');   // <--- memory usage around 500mb
x = null;
alert('done');

And if you try "x= null;" instead of delete ?

Just assign null to the variable:

x = null;

I realize you mentioned the data is throw away, but, when you delete the nodes, even if just setting x to null, you need to make certain that no event handlers are attached to any of the nodes, otherwise that node cannot be garbage collected.

Here is a function I use in my own code: http://javascript.crockford./memory/leak.html