You can find all the information that you need at the webpage: https://developer.chrome.com/devtools/docs/javascript-debugging

By simply putting it (copied from the webpage)
Open a site such as the Google Closure hovercard demo page or the TodoMVC
Open a site such as the Google Closure hovercard demo page or the TodoMVC Angular app
Open the DevTools window.
If it is not already selected, select Sources.
Debugging with breakpoints
A breakpoint is an intentional stopping or pausing place in a script. Use breakpoints in DevTools to debug JavaScript code, DOM updates, and network calls.
Add and remove breakpoints In the Sources panel, open a JavaScript file for debugging. In the example below, we are debugging the todoCtrl.js file from the AngularJS version of TodoMVC.
Click the line gutter to set a breakpoint for that line of code. A blue tag will indicate if a breakpoint has been set:

With the above simple example you can actually "stop" the function getCurrentPosition()
and debug it.