By Karl Voelker

JavaScript:

• is the original implementation of the ECMAScript standard,
• looks a bit like, but is otherwise unrelated to, Java,
• is dynamically-typed,
• is object-oriented (but strangely), and
• has first-class functions.

The most common use of JavaScript is in web browsers, but:

• The language has no web-specific features.
• Browser interaction is done through libraries provided by the browser.

We will look at the language first.

Numeric and logical operators are basically the same as in C/C++/Java:

Some operators are overloaded to work on strings:

Other numeric and logical operators cause a conversion to Number or Boolean:

To get the length of a string, use .length.

This is not a method call; it's a magical property:

x = "foo";
xlen = x.length;   // correct
xlen = x.length(); // incorrect

//returns null:
"foo".match(/bar/);

//returns ["f"]:
"foo".match(/f/);

// returns ["foo", "f", "oo"]
"foo".match(/(f)(o+)/);

// returns "foo"
"foo".replace(/x/, "g");

// returns "goo"
"foo".replace(/f/, "g");

// returns "foo 1"
"foo 4".replace(/\d+/, 
    function (s) { return s % 3 });

In JavaScript's "for each" construct, the loop variable takes on the key (or index) at each step, not the value:

x = {foo: 3, bar: 2};
for (k in x) {
	// k will be "foo", then "bar"
}

y = [5, 6];
for (k in y) {
	// k will be 0, then 1
}

These control structures work just like in C/C++/Java:

• for (when not used as "for each")
• while
• if/else

By default, any variable you use is global. To declare a lexically-scoped variable:

var x;

var y = 5;

Semicolons are almost never required.

There are a few ways JavaScript can be included in a web page:

Script file

Hyperlink

Foo

Event handler

Foo

JavaScript is object-oriented, but has no classes.

An object may be given a prototype, which is just another object.

If you look for a method or attribute in an object, and it doesn't have it, it will ask its prototype.

The Mozilla Developer Center has some good references:

http://developer.mozilla.org/en/docs/JavaScript