JavaScript: The Good Parts
@jonathanjulian

crockford.com

First, the Bad Parts

globals. optional ;
truthy/falsy. scope.

Then, the Good Parts!

functions as objects. loose typing.
dynamic objects. literals.

The Bad Parts

globals
• x = 1;
• var y = 1;
• x is in the global namespace
• YourAppName.x = 1;

line termination
• semi-colons are INSERTED by the parser
• optional semi-colons are not a “language
feature”
• you are not warned

truthy / falsy

==

===
All of these are false

take advantage
• if (x)
• if (myobject.propery)
• if (myobject.property == null) // no, No, NO!
• test for exactly what you want to test for
• ...or not
• KNOW THE FALSY VALUES
undefined, null, false, 0, ‘’, NaN

no block scope
• functions create scope
• blocks do not

The Good Parts!

functions are objects
• can be passed, returned
• have scope
• have closure

loose typing
• no compiler
• no type heirarchies

objects are dynamic
• members can be added to any object, any time
• helpful to attach attributes

object literals
• aka JSON
• { count: 2, prefix: ‘pre_’ }
• pass options to functions
• JSON as communication
• JSON as persistence
• etc

Know the bad parts are
there...and avoid them

Learn and love the
good parts!

tools
• FireBug
• JSLint
• spidermonkey / rhino / v8

takeaway
• think about vars and scope
• never use ==
• if (myobject) {
• jslint.com

JavaScript is a beautiful
language

jonathan.m.julian@gmail.com
@jonathanjulian
jonathanjulian.com