JavaScript

Sejarah

Pada asalnya, pembangunan JavaScript diusahakan oleh Brendan Eich di bawah nama Mocha, kemudiannya ditukar kepada LiveScript, dan akhirnya ditukar kepada JavaScript. Perubahan nama dari LiveScript ke JavaScript adalah berkebetulan dengan langkah Netscape menambah sokongan teknologi Java di pelayar web Netscape Navigator keluarannya. JavaScript mula diperkenalkan dan dipasang di pelayar Netscape versi 2.0B3 pada Disember 1995.
Pada tahun 2011, versi terakhir bagi JavaScript ialah 1.8.5

Contoh mudah

Fungsi rekursif ringkas:
function factorial(n) {
    if (n === 0) {
        return 1;
    }
    return n * factorial(n - 1); 
}
Skrip aluan ringkas:
var nama = prompt("Nama anda siapa?");
alert("Selamat datang "+nama);
Sintaks fungsi awanama (atau lambda):
function add (i, j) {
    var add_pri = function (x, y) {
        return x + y;
    };
 
    return add_pri(i, j);}
Penutupan:
function showclosure () {
    var inc = makeinc(1);
 
    inc(); // 1
    inc(); // 2
    inc(); // 3}
 
function makeinc (initialValue) {
    var count = initialValue;
 
    return function () {
        return count++;
    };}
Demonstrasi fungsi variadik. 1 akan dialert, kemudian 2, seterusnya 3. arguments merupakan pemboleh ubah khas.
function unlimited_args () {
    for (var i = 0; i < arguments.length; i++) {
        alert(arguments[i]);
    }}
 
unlimited_args(1, 2, 3);

Contoh yang lebih rumit

Kod sampel ini menunjukkan pelbagai tampilan-tampilan JavaScript.
/* 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"); // exception throwing
        }
        return x;
    };
    this.a = checkInt(x)
    // ^ semicolons are optional (but beware since this may cause consecutive lines to be
    //erroneously treated as a single statement)
    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 predefined in JavaScript 1.6.// They are currently not available in the JScript engine built into// Microsoft Internet Explorer, but are implemented in Firefox, Chrome, etc.// 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) {
    /* Note: print() is a JS builtin function available in Mozilla's js CLI;
     * It is functionally equivalent to Java's System.out.println().
     * Within a web browser, print() is a very different function
     * (opens the "Print Page" dialog),
     * so use something like document.write() or alert() instead.
     */
    // print       (obj + ", gcd = " + obj.gcd() + ", lcm = " + obj.lcm());
    // alert       (obj + ", gcd = " + obj.gcd() + ", lcm = " + obj.lcm());
    document.write(obj + ", gcd = " + obj.gcd() + ", lcm = " + obj.lcm() + "<br />");});
Keluaran berikut sepatutnya akan dipaparkan pada tetingkap pelayar.

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
Jika Internet Explorer digunakan, contoh tadi akan menghasilkan ralat. Dengan itu, contoh tadi menunjukkan bahawa pentafsir JScript bagi Internet Explorer melakukan kod dengan cara berbeza berbanding pentafsir JavaScript dan ECMAScript dalam pelayar web lain. (Lihat ulasan dalam kod sumber untuk perincian perbezaan yang relevan bagi contoh ini.)