debugging javascript (by thomas bindzus, founder, vinagility & thanh loc vo, cto, epsilon mobile...

Debugging JavaScriptClient side scripting

Outline

1. Debugging toolsa. Built-ins and beyond, but mostly built-ins

2. Fishbone diagram

3. Debugging workshop

Getting started with debugging JS

1. Brower built-insa. Chrome, Safari, Opera, Firefox, IE

2. Browser extensiona. Firebug (lite) (Firefox, IE6+, Opera, Safari, Chrome)

3. External debugger applicationa. Weinre

BIAS ALERT!!

The code we’ll be using

● index.html○ Gluing it all together

● script.js○ Declaration of our DebuggerExamples object

● style.css○ Nothing stylish :-)

Breaking the code - Statically

Static breakpoints using the debugger keyword…breakthru: function() { // Queen debugger; …}… Don’t do this!

Show me the code!

Breaking the code - Dynamically

Dynamic breakpoints

Best practice!

The pain of minified JavaScript

But my JavaScript is minified I can’t break in it?!

YES YOU CAN! :-)

The JavaScript GPS

● Navigate the code● Get your position● Breakpoints

○ Code○ DOM○ XHR○ Event listener

?

The console.log command

● console.log('Most developers know this')

● console.log('And even ', this)

● console.log('What %s this %d?', 'about', 1)

● What is the output?!

Some more console commandsCommand What is the result?

inspect >inspect(document.body)

$0 >$0

$_ >$_

copy >copy($_)

dir >dir($0)

clear >clear()Bonus question (given that jQuery is present):

>inspect($)

Want to learn more?

● Some resources○ https://developers.google.com/chrome-developer-tools/docs/tips-and-tricks

○ http://www.paulirish.com/2011/a-re-introduction-to-the-chrome-developer-tools/

○ http://www.paulirish.com/2011/quick-color-manipulation-with-the-chrome-devtools/

○ http://www.randomthink.net/blog/2012/11/breakpoint-actions-in-javascript/

○ http://www.youtube.com/watch?v=nOEw9iiopwI

○ http://www.youtube.com/watch?v=N8SS-rUEZPg&feature=youtu.be

● And of course much of the same is possible in Firebug

○ http://lmgtfy.com/?q=Firebug+tips+and+tricks

Fishbone diagram

● Other name: Ishikawa diagram.● Used for cause and effect analysis.

Fishbone diagram (2)

Fishbone diagram (3)1. Collect all the effect of the errors.2. With each effect, identify all the possible causes.3. Analyze the causes, just to group and prioritize them.4. Pick a cause from the list in prioritized order, make a

solution, then implement it. 5. If the error wasn’t been solved, back to step #4.

Pros for using the process?

● Help you to have an overview of the problem.

● Easier to call for help, as well as better collaboration.

● When you can’t discover the issue, you know why. My code broke, and I don’t know why...

Cons

Take times….

Questions?

Workshop

Problem #1

http://jsfiddle.net/jECLf/1/

Problem #2 http://jsfiddle.net/t45UM/

Problem #3

What is the problem, and how to fix?http://jsfiddle.net/Q7vhS/

http://jsfiddle.net/Q7vhS/embedded/result/

Problem #4var elements = [1,2,3,4,5,6,7,8,9];

$(elements).each(function(i, e) {

var row;

if (i % 3 == 0) {

row = $('<div>').appendTo('body');

}

$('<span>' + e + '</span>').appendTo(row);

});

I want to create a grid with 3 elements

in each row. This code relies on

jQuery, but there is something wrong,

can you spot it?

● http://tobyho.com/2011/11/16/7-common-js-mistakes-or-confusions/

● http://tobyho.com/2011/11/09/life-without-compiler/

● http://tobyho.com/2011/11/11/js-object-inheritance/

● http://net.tutsplus.com/tutorials/javascript-ajax/the-10-javascript-mistakes-youre-making/

● http://nullprogram.com/blog/2012/11/19/

● http://www.elijahmanor.com/2011/08/7-chrome-tips-developers-designers-may.html

References

Presentation made for “Javascript Ho Chi Minh City” meetup group

You can find us at:● http://meetup.com/JavaScript-Ho-Chi-Minh-City/● https://www.facebook.com/JavaScriptHCMC● https://plus.google.

com/communities/116105314977285194967

Thank you