As a Java developer, I used to hate JavaScript. At one time I used to say “friends don’t let friends use JavaScript”.

In recent years, JavaScript has become required for a flexible & feature rich user experience. WIth the advent of tools such as JQuery and GWT many of these issues have been minimized. Also, I took the time to read more about JavaScript. The book that really opened my eyes is JavaScript: The Good Parts.

So… What do Java developers hate?

JavaScript may look like Java, smell like Java and even taste a little like Java, but it does not behave like Java

Variables are global in scope

“this” has different meaning based on the invocation type (learn this for your own sake)

Braces do NOT guarantee scope

Functions are first class citizens, not classes (avoid classes, you will set yourself up for disappointment)

Functions are objects, not simply methods to a class

Variables are dynamically typed objects

JavaScript often fails silently (this is for user experience)

Difficult to debug (use FireFox & Firebug addon)

Semicolons are optional (bad idea, put them where you want them)

Functions always return values, a value or “undefined”

“new” has some specific assumptions, not simply creating an Object

Cross browser compatibility (use jQuery or GWT to address most issues)

What should you understand about JavaScript?

Functions – First class citizens, the primary object in JavaScript

prototype system – Object.prototoype, object linkage, delegation, hasOwnProperty() method, etc.

closures

currying

the 4 invocation types: method, function, constructor & apply

dynamic languages such as groovy, ruby, etc. they share many similarities

What should you forget when using JavaScript?

Classes

Scope using braces

Strong typing

In summary, it is an entirely different language with many syntactical similarities. JavaScript is very power and flexible once you understand how it behaves. I highly recommend the O’Reilly book (mentioned above), its a short read and packed with awesome facts.