[javascript] Is it possible to change javascript variable values while debugging in Google Chrome?

I'm debugging a javascript app (using Chrome dev tools), and I would like to change some variable values while stepping through the code.

Is that possible at all?

I have tried and got something like:

> modeline
1
> modeline=0
0             <<< seems to work but... 
> modeline
1             <<< ups!!

But I'm unable to find any documentation that states what can or can't be done...

I don't know why chrome team don't allow this silly feature ... but the only way I could change variable values with success is to modify the script directly in the chrome editor under "Sources" Tab (this changes the behavior of your script until you refresh the page), but that changes will lost when refresh, so be carefull.

I'm able to modify a script variable value by assignment in the Console. Seems simplest.

To modify a value every time a block of code runs without having to break execution flow:

The "Logpoints" feature in the debugger is designed to let you log arbitrary values to the console without breaking. It evaluates code inside the flow of execution, which means you can actually use it to change values on the fly without stopping.

Right-click a line number and choose "Logpoint," then enter the assignment expression. It looks something like this:

I find it super useful for setting values to a state not otherwise easy to reproduce, without having to rebuild my project with debug lines in it. REMEMBER to delete the breakpoint when you're done!

I was having the same issue, went to the 'About Google Chrome'->Help and it said I needed to restart my browser to get the latest updates.

I did this, and suddenly, I can now change local variables. Simply click the variable you want to edit in the Scope Variables window, and type in your new value.

I did notice some oddities though, that I had to step over some unrelated var assignments before I could alter the text in the right hand window (Scope Variables).

It looks like not.

Put a breakpoint, when it stops switch to the console, try to set the variable. It does not error when you assign it a different value, but if you read it after the assignment, it's unmodified. :-/

Actually there is a workaround. Copy the entire method, modify it's name, e.g. originalName() to originalName2() but modify the variable inside to take on whatever value you want, or pass it in as a parameter.

Then if you call this method directly from the console, it will have the same functionality but you will be able to modify the variable values.

If the method is called automatically then instead type into the console

originalName = null;
function originalName(original params..)
{
    alert("modified internals");
    add whatever original code you want
}

Yes! Finally! I just tried it with Chrome, Version 66.0.3359.170 (Official Build) (64-bit) on Mac.

You can change the values in the scopes as in the first picture, or with the console as in the second picture.

Firebug seems to allow you to do that.

This is an acknowledged bug in the Chrome Dev Tools:

http://code.google.com/p/chromium/issues/detail?id=124206

This is now possible in chrome 35 (today as of July 11, 2014). I don't know which version allowed it first though.

Just tested @gilly3 example on my machine and it works.

• Open the console, in Sources and the tab Snippets, add a new snippet, paste the following code into it:

  var g_n = 0; function go() { var n = 0; var o = { n: 0 }; return g_n + n + o.n; // breakpoint here }

• Right-click the snippet name, click 'Run' (this does not fire the function though)

• Add the breakpoint at the return statement.
• In the console below, type go()
• and change the variable values as demonstrated below

and the returned result g_n + n + o.n is 30.