break on access to a property
JavaScript HTML
Switch branches/tags
Nothing to show
Clone or download
Latest commit 49440c4 Mar 8, 2018


Omg the cookie is being changed, but where? Give me a breakpoint when JS changes my cookies!

breakOn(document, 'cookie');

Some JS is getting the scrollTop value causing massive Recalculate Styles costs. Who is the perpetrator PERFetrator?

breakOn(document.body,'scrollTop', 'read')

This works really well as a snippet in the Chrome DevTools:

By default, breakOn will only break when JS attempts to change the value of a property. The third optional argument takes 'read' if you'd also like to break when values are read.

It is also possible to disable/enable a breakpoint by using methods provided by returned object.

    var bp = breakOn(document, 'cookie');
    // found it!
    // something else is up....

breakOn also supports Conditional Breakpoints when the 4th argument is a function. Say you know a property is being changed after the 4th change.

    var i = 0;
    var bp = breakOn(document, 'cookie', false, function(v) {
        return i++ >= 4;

Or something is leaving a property undefined

    var bp = breakOn(document, 'cookie', false, function(v) {
        return typeof v === 'undefined';


Dave Methvin, Paul Irish, fat, and these handsome people



Object.defineProperty(twttr, 'profile', {
    get: function () {
  , set: function (val) {