Debugging JavaScript with Chrome

Debugging JS with Chrome
>The little power tools
Igor Zalutsky

Async call stacks
setTimeout(function () {
$.ajax({
url: 'http://echo.jsontest.com/foo/bar'
}).done(function(response) {
debugger;
});
}, 500);

Console API: the basics
var obj = {
prop: 1, child: {
prop: 2
}
};
console.log(obj);
console.log('%On%o', document.body, document.body);
console.warn('something unexpected happened');
console.error('something went wrong');
console.assert("str" instanceof String, 'gotcha!');

Console API: time() and count()
function fibonacci(n) {
return (n > 1) ? fibonacci(n - 2) + fibonacci(n - 1) : n;
}
console.time('fibonacci');
console.log(fibonacci(30));
console.timeEnd('fibonacci');
document.addEventListener('keydown', function(event) {
console.count(String.fromCharCode(event.keyCode));
});

Console from the inside
console.dir(console);
?

Console API: table()
var people = [
{
name: 'Hopper', surname: 'Herring'
}, {
name: 'Sampson', surname: 'Douglas'
}, {
name: 'Carmella', surname: 'Vincent'
}
];
console.table(people);
console.table(
document.querySelectorAll('a'),
['href', 'text']
);

Console API: other methods
clear() remove all previous output
debug(), info() aliases for log()
group(), groupEnd() grouped output
profile(), profileEnd() last evaluated expression
timeStamp() marking the timeline
trace() stack trace

Digging out Command Line API
(function() {
debugger;
})();
var members = Object.keys(__commandLineAPI)
.filter(function(key) {
return ! (key in console);
}).reduce(function(obj, key) {
obj[key] = __commandLineAPI[key];
return obj;
}, {});
console.dir(members);

Command Line API: shortcuts
$(selector) document.querySelector()
$$(selector) document.querySelectorAll()
$_ last evaluated expression
$0 - $4 last 5 inspected DOM nodes or heap entries
$x(path) XPath query

Command Line API: monitoring events

Command Line API: hidden hooks

Command Line API: other methods
copy(object) copies string representation to clipboard
inspect(object) shows object in DOM inspector or profiler
getEventListeners(object) returns hash of arrays of listeners
profile(), profileEnd() last evaluated expression
keys(object) same as Object.keys(object)
values(object) returns array of object’s values

Thanks!
Useful links
> Google Chrome Console API docs
> Google Chrome Command Line API docs
> “Lesser-Known JavaScript Debugging Techniques” by Amjad Masad
> “Advanced JavaScript Debugging with console.table()” by Marius Schulz
Follow me!
@igorzij github.com/zij linkedin.com/in/izalutsky

Debugging JavaScript with Chrome

More Related Content

What's hot

Viewers also liked

Similar to Debugging JavaScript with Chrome

Recently uploaded

Debugging JavaScript with Chrome