This is a summarized form of the JavaScript Tutorial.

For reference JavaScript specifications can be found here .

• 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

  <script type="text/javascript">
  <!--
  document.write("Hello World!");
  //-->
  </script> 

• 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>

• 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.

• 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.

• 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

• Objects have properties and methods.
• Objects can be created directly

  personObj=new Object();
  personObj.firstname="John";
  personObj.newfirstname =
   function (new_firstname)
     { this.firstname=new_firstname; } 

• Objects can be created using a template

  function person(firstname) {
    this.firstname=firstname;
    this.newfirstname =
      function (new_firstname)
      { this.firstname=new_firstname; }
  }
  myFather=new person("John");

• Object methods can also be assigned by name e.g.

  function person(firstname)
  {
    this.firstname=firstname;
    this.newfirstname=newfirstname;
  }
  function newfirstname(new_firstname)
  { this.firstname=new_firstname; } 

• 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

   var mycars=new Array("Saab","Volvo","BMW");

• Arrays have methods including: sort, concat, join.
• To sort an integer array, must use a function

   function intSort (a, b){ return a - b;}

• 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.

• navigator.appName/appVersion contain the browser name and version.
• document.cookie allows read and write access to cookie so to set a cookie

  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());
  } 

• 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 :

  document.getElementById("block_id").innerHTML=txt;

• To set or clear a timed action:

  var t=setTimeout("javascript statement",milliseconds);
  clearTimeout(t);