JavaScipt examples extracted from MSDN 's reintroduction.

gistfile1.js

// The && and || operators use short-circuit logic, which means whether they will execute their second operand is dependent on the first. This is useful for checking for null objects before accessing their attributes:

var name = o && o.getName();


// Or for setting default values:

var name = otherName || "default";


//JavaScript has a ternary operator for conditional expressions:

var allowed = (age > 18) ? "yes" : "no";



for (var i = 0; i < a.length; i++) {
    // Do something with a[i]
}
// This is slightly inefficient as you are looking up the length property once every loop. An improvement is this:
 
for (var i = 0, len = a.length; i < len; i++) {
    // Do something with a[i]
}
An even nicer idiom is:
 
for (var i = 0, item; item = a[i++];) {
    // Do something with item
}



// “Named anonymous functions” as below:

var charsInBody = (function counter(elm) {
    if (elm.nodeType == 3) { // TEXT_NODE
        return elm.nodeValue.length;
    }
    var count = 0;
    for (var i = 0, child; child = elm.childNodes[i]; i++) {
        count += counter(child);
    }
    return count;
})(document.body);



// Attaching functions to objects

function makePerson(first, last) {
    return {
        first: first,
        last: last,
        fullName: function() {
            return this.first + ' ' + this.last;
        },
        fullNameReversed: function() {
            return this.last + ', ' + this.first;
        }
    }
}
> s = makePerson("Simon", "Willison")
> s.fullName()
Simon Willison
> s.fullNameReversed()
Willison, Simon




// We can take advantage of the ‘this’ keyword to improve our makePerson function:

function Person(first, last) {
    this.first = first;
    this.last = last;
    this.fullName = function() {
        return this.first + ' ' + this.last;
    }
    this.fullNameReversed = function() {
        return this.last + ', ' + this.first;
    }
}
var s = new Person("Simon", "Willison");




// Prototypes 

function Person(first, last) {
    this.first = first;
    this.last = last;
}
Person.prototype.fullName = function() {
    return this.first + ' ' + this.last;
}
Person.prototype.fullNameReversed = function() {
    return this.last + ', ' + this.first;
}



// Closures 

function makeAdder(a) {
    return function(b) {
        return a + b;
    }
}
x = makeAdder(5);
y = makeAdder(20);

x(6) // returns 11
y(7) // returns 27