===== Javascript Cheat Sheet =====

This is a summarized form of the [[http://www.w3schools.com/js/default.asp | JavaScript Tutorial]].

For reference JavaScript specifications can be found [[http://developer.mozilla.org/en/JavaScript_Language_Resources | here]] .

==== What is Javascript ====

  * JavaScript is the most popular scripting language on the internet and works in all major browsers.
  * It is a lightweight, interpreted, object-oriented language that is embedded into webpages to add interactivity.
  * JavaScript can read and write HTML page elements, react to events, validate data, create cookies.
  * JavaScript was invented by Brendan Eich of Netscape but is now known officially as ECMAScript (current version is ECMA-262).
  * A simple "Hello World" example <code html>
<script type="text/javascript">
<!--
document.write("Hello World!");
//-->
</script> </code>
  * JavaScript code may be located
    * In the head - executed when called
    * In the body - executed while loading
    * In an external file called from either the head or the body e.g. <script src="abc.js"></script>

==== Basic Syntax ====

  * JavaScript is case-sensitive.
  * Statements may omit the final semi-colon but should not.
  * Blocks may be grouped together using curly braces { }.
  * JavaScript uses java-style comments: %%//%% and /* */.
  * JavaScript variables are case-sensitive and must begin with a letter or underscore.
  * Variables are automatically declared when first used but should be explicitly declared using e.g. var a = 5;
  * JavaScript uses standard C/Java operators e.g. +-*/%, ++, +=, &&, ||, !, + (concatenation).
  * JavaScript uses C/Java comparators >,>=,==, !=, a?b:c. It also uses === to test equality of value and type.

==== Basic Structures ====

  * if {} else if {} else {}
  * for (var=start;var%%<=%%end;var=var+inc) {}
  * while (condition) {}
  * do {} while (condition) ;
  * //break// and //continue// both valid in a loop.
  * for (element in array) {}
  * for (property in object) {}
  * switch (n) { case 1: stmt; break; default: stmt; }
  * function name(var1,var2,...) {}
  * \", \n, \t, \r, \', \&, \\
  * with (object) { } changes default object for fields.

==== Events, Error Handling & Popups ====
  *  try { throw "errname"; } catch(err) {}
  * onerror=handleErr; handleErr(msg,url,linenum)
  * if handleErr returns false, browser displays a standard error message in the JavaScript console.

  * an alert box just has an OK button - alert("msg")
  * a confirm box returns true if the user clicks OK, false if he clicks cancel - confirm("msg")
  * a prompt box allows the user to enter a value. It returns true if the user clicks OK, false if he clicks cancel - prompt("msg","defaultvalue");

  *  JavaScript functions can be registered to run on certain events (event="jscode" in an HTML element):
    * onunload, onload (page or image), onresize, onabort
    * onfocus, onblur, onclick, ondblclick
    * onmouseover, onmouseout, onmousemove
    * onchange, onsubmit, onreset, onselect
    * onkeydown, onkeypress, onkeyup
    * onmousedown, onmouseup

==== JavaScript Objects ====
  * Objects have properties and methods.
  * Objects can be created directly <code javascript>
personObj=new Object();
personObj.firstname="John";
personObj.newfirstname =
 function (new_firstname)
   { this.firstname=new_firstname; } </code>
  * Objects can be created using a template <code javascript>
function person(firstname) {
  this.firstname=firstname;
  this.newfirstname =
    function (new_firstname)
    { this.firstname=new_firstname; }
}
myFather=new person("John");</code>
  * Object methods can also be assigned by name e.g. <code javascript>
function person(firstname)
{
  this.firstname=firstname;
  this.newfirstname=newfirstname;
}
function newfirstname(new_firstname)
{ this.firstname=new_firstname; } </code>

==== Predefined Objects ====
  * String objects have a length property and methods including: indexOf, match, replace
  * new Date() creates a Date object (with today's date).
  * Date objects include methods: getTime(epoch), setFullYear, toUTCString, getDay, getHours
  * Date objects can be compared using <, > .
  * To declare an array <code javascript> var mycars=new Array("Saab","Volvo","BMW");</code>
  * Arrays have methods including: sort, concat, join.
  * To sort an integer array, must use a function <code javascript> function intSort (a, b){ return a - b;}</code>
  * The Math object contains common math routines: round, random, e, pi etc.
  * The RegExp object supports regexp creation and searching including methods: test (t/f), exec, compile (alter).
  * HTML DOM objects allow access to browser and webpage.

==== Advanced JavaScript ====
  * navigator.appName/appVersion contain the browser name and version.
  * document.cookie allows read and write access to cookie so to set a cookie <code javascript>
function setCookie(c_name,value,expiredays)
{
  var exdate=new Date();
  exdate.setDate(exdate.getDate()+expiredays);
  document.cookie=c_name+ "=" +escape(value)+
    ((expiredays==null) ? "" :
     ";expires="+exdate.toGMTString());
} </code>
  * The onsubmit event can be used to validate a form.
  * document.img_name.src ="pic.gif" changes an image.
  * To change the content of a block with a given id : <code javascript>
document.getElementById("block_id").innerHTML=txt;</code>
  * To set or clear a timed action: <code javascript>
var t=setTimeout("javascript statement",milliseconds);
clearTimeout(t); </code>