javascript code samples

Simple examples

A simple recursive function:

function factorial(n) {

    if (n == 0) {

        return 1;

    }

    return n * factorial(n - 1);

}

A simple personalised greeting script:

var name = prompt("What is your name?");

alert("Welcome " + name);

Anonymous function (or lambda) syntax:

function add(i, j) {

    var addLambda = function(x, y) {

        return x + y;

    };

    return addLambda(i, j);

}

Closures:

function displayClosure() {

    var inc = makeIncreaser(1);

    inc(); // returns 1

    inc(); // returns 2

    inc(); // returns 3

}

function makeIncreaser(init) {

    var count = init;

    return function() {

        return count++;

    };

}

Variadic function demonstration. This will alert with 1 then 2 then 3. arguments is a special variable.

function unlimitedArgs() {

    for (var i = 0; i < arguments.length; ++i) {

        alert(arguments[i]);

    }

}

unlimitedArgs(1, 2, 3);

More advanced example

This sample code showcases various JavaScript features.

/* Finds the lowest common multiple of two numbers */

function LCMCalculator(x, y) { // constructor function

    var checkInt = function (x) { // inner function

        if (x % 1 !== 0) {

            throw new TypeError(x + "is not an integer"); // throw an exception

        }

        return x;

    };

    this.a = checkInt(x)

    // ^ semicolons are optional

    this.b = checkInt(y);

}

// The prototype of object instances created by a constructor is

// that constructor's "prototype" property.

LCMCalculator.prototype = { // object literal

    constructor: LCMCalculator, // when reassigning a prototype, set the constructor property appropriately

    gcd: function () { // method that calculates the greatest common divisor

        // Euclidean algorithm:

        var a = Math.abs(this.a), b = Math.abs(this.b), t;

        if (a < b) {

            // swap variables

            t = b;

            b = a;

            a = t;

        }

        while (b !== 0) {

            t = b;

            b = a % b;

            a = t;

        }

        // Only need to calculate GCD once, so "redefine" this method.

        // (Actually not redefinition - it's defined on the instance itself,

        // so that this.gcd refers to this "redefinition" instead of LCMCalculator.prototype.gcd.)

        // Also, 'gcd' == "gcd", this['gcd'] == this.gcd

        this['gcd'] = function() {

            return a;

        };

        return a;

    },

    "lcm"/* can use strings here */: function() {

        // Variable names don't collide with object properties, e.g. |lcm| is not |this.lcm|.

        // not using |this.a * this.b| to avoid FP precision issues

        var lcm = this.a / this.gcd() * this.b;

        // Only need to calculate lcm once, so "redefine" this method.

        this.lcm = function() {

            return lcm;

        };

        return lcm;

    },

    toString: function () {

        return "LCMCalculator: a = " + this.a + ", b = " + this.b;

    }

};

// Note: Array's map() and forEach() are defined in JavaScript 1.6.

// They are used here to demonstrate JavaScript's inherent functional nature.

[[25, 55],[21, 56],[22, 58],[28, 56]].map(function(pair) { // array literal + mapping function

    return new LCMCalculator(pair[0], pair[1]);

}).sort(function(a, b) { // sort with this comparative function

    return a.lcm() - b.lcm();

}).forEach(function(obj) {

    document.write(obj + ", gcd = " + obj.gcd() + ", lcm = " + obj.lcm() + "<br>");

});

The following output should be displayed in the browser window.

LCMCalculator: a = 28, b = 56, gcd = 28, lcm = 56

LCMCalculator: a = 21, b = 56, gcd = 7, lcm = 168

LCMCalculator: a = 25, b = 55, gcd = 5, lcm = 275

LCMCalculator: a = 22, b = 58, gcd = 2, lcm = 638

This obfuscated example writes "Hello World"; it is made to be copy/pasted into the web address bar.

javascript:var AZ=new Array("A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z", " "); var az=new Array("a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z", " "); document.write(AZ[7],az[4],az[11],az[11],az[14],AZ[26],AZ[22],az[14],az[17],az[11],az[3])

This is the same code adapted to html markup.

<script type="text/javascript">

//Creates the capital letters

var AZ=new Array("A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z", " ");

//Creates the lowercase letters

var az=new Array("a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z", " ");

//writes the text based on AZ and az

document.write(AZ[7],az[4],az[11],az[11],az[14],AZ[26],AZ[22],az[14],az[17],az[11],az[3])

</script>