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===== 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 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">

</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, \', \&, \\

==== Events, Error Handling and 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 ====
  * JavaScript is an Object Oriented Programming Language.
  * Objects have properties and methods.
  * 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 html> 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 html> function intSort (a, b){ return a - b;}</code>
  * The Math object contains common math routines: round, random, e, pi etc.

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