This document discusses JavaScript functions and related concepts. It defines functions, classes, and methods. It shows how functions can take arguments, be passed as callbacks, return other functions, and create closures. Classes can be defined using functions with the new keyword or by adding to prototypes. Built-in types like Number, String, and Array can be constructed or assigned directly. Functions are first-class objects that can be assigned and passed around.

1. JavaScript function

2. Define a functionfunction f(msg) {alert(msg);}// overridefunction f(msg1, msg2) {alert(msg1 + ' ' + msg2);}// arguments keywordfunction f() { for (var i = 0; i < arguments.length; i ++ ) { alert(arguments[i]);}}// callf();

3. Define a classvarMyAlert = function (msg) { this.msg = msg;// define a methodthis.f = function () { alert('Hello ' + this.msg); };};varmyalert = new MyAlert('Mary');// call f methodmyalert.f();

4. Define a class by prototypevarMyAlert = function (msg) { this.msg = msg;};// use prototype to define a methodMyAlert.prototype.f = function () { alert(this.msg);};prototype definition uses less memory

5. Built-in typesNumbervarnum = new Number(2); or varnum= 2; Objectvarobj = new Object(); or varobj = {}; Arrayvararr = new Array(1, 2, 3); or vararr = [1, 2, 3];Stringvarstr = new String('Hello'); or varstr = 'Hello';Regular expressionvar regex = new RegExp('\s*'); or varregex = /\s*/;etc... - w3schools.com/js

6. String prototypeString.prototype.f = function () { alert(this);};varstr = 'Hello Mary';str.f();

7. Define a function (more)// goes to top of current scopefunction f(msg) { alert(msg);}// assignmentvarf = function (msg) { alert(msg);};// use new keywordvar f = new Function('msg', 'alert(msg);');

8. Function prototypeFunction.prototype.f= function () { alert(this.toString());};var f = function () { alert('This is a function.');};// does NOT alert "This is a function." f.f();

9. Anonymous function(function (msg) { alert('This is ' + msg);})('anonymous');(function (msg) {// this line does NOT get executed alert('This is ' + msg);}).f();

10. Callbackfunction f(callback) { callback();}function dosomething() { alert('This is a callback function.');}f(dosomething);

11. Return a functionfunction f() {varnum= 1;// num can be accessed in inner functionvarinnerf = function () {alert( 'inner function called, num: ' + num); }; return innerf;}// f2 now is a functionvarf2 = f();f2();

12. Closurefunction f() {varnum= 1;// num can be accessed in inner functionvarinnerf = function () {num ++; alert( 'inner function called, num: ' + num ); }; return innerf;}// f2 now is a functionvar f2 = f();f2();

13. SummaryFuntionis a objectused to create classcan be passed as parametercan be returnedcreates a closure when defined in another function