Break on a change of variable value

Question

Similar to other questions here, like this one.

Is there a way to break on the change of a variable value in any JavaScript debugger? (like IE Developer tools, Visua

Answer 1

I don't know if I misunderstood your question. If you want to watch an expression and stop when it reaches a certain value while in a js debugging session in Chrome Developer Tools, it's rather trivial.

You can simply put a breakpoint on the line where the value you want to check is, then click with right mouse button on it and select "Edit breakpoint...". A dialog will pop up prompting for an expression, where execution will stop when its value its true.

For instance, let's say you have a loop and you are adding one unit to a variable inside it and want to stop execution when the variable equals to 3. The expression in loop would look like this:

n = i++;

You must set your breakpoint on that line and the expression to watch (after prompted by "Edit breakpoint...") would be n == 3. When running your code it will stop there when your variable reaches that value.

You'll notice your condition is set because your breakpoint turns orange instead of blue.