You can use the console to add assertion messenges
console.assert(booleanCondition, "Failed Assertion.");
Will display an error only if booleanCondition evaluates to false.
More console Chrome tips @ http://goo.gl/MNYZd
Only for me it's console.assert(), not assertion. Using Chrome Version 25.0.1364.172
@dpashkevich tnx... I was so exited... that I misspelled :-(