Insert break point into a javascript file

Question

I would like to insert break point at a position listed in the below quote. Let's say the below quote belongs to a js file called "test.js". What I would like to do is when I run "node test.js" on the command line, it will break at the break point and then I can inspect all the variables available at the break point.

var a = 4;

function changeA(input) {
  var input = 6
  [INSERT BREAK POINT HERE]
  console.log(input)
};

changeA(a);
console.log(a);

Or is there another way to insert break point to a javascript file?

Answer 1

You can hardcode a breakpoint like this:

debugger;

E.g.:

function changeA(input) {
  var input = 6
  debugger;
  console.log(input)
}

...but you have to be using a debugger for it to mean anything, such as node-inspector. And if you're using a debugger, you can set breakpoints through the debugger itself (rather than hardcoding them).

Here's an example of debugging a very simple NodeJS script via node-inspector:

Script:

var a = +process.argv[2];
var b = +process.argv[3];
var c = a + b;
console.log("c = " + c);

Command to start node-inspector and pass my script a couple of args:

node-debug temp.js 10 20

A browser pops up with a debugging UI and the program paused. I've set a breakpoint through the UI on the var b = ... line, and then stepped passed it once, so I'm sitting on the var c = a + b; line (which hasn't run yet):