JavaScript - some thoughts & notes

No relationship to Java
(except loose one that a lot languages have by coming after C)

can go in body or head tho' there are some differences as to when they get loaded

<script> ... </script>

pull code in from another file (IN THE SAME FOLDER) with

<script src='otherJavaScriptFile.js'></script>

pull code in from another file (SOMEWHERE ON THE WEB) with

<script src='http://someserver.com/otherScriptFile.js'></script>

have DOM objects listen for the code by adding to their ... attributes

<body onload="...
              javascript goes here. NO script tags! but quotes reqired
              ...
             ">

    <button onclick="...
                    javascript goes here. NO script tags! but quotes reqired
                    ...
                   ">
      Press Here
    </button>

TIAS - BUTTONS & OBJECTS

do not require trailing SEMI-COLONS however ...
Dr Dale often will "Use them out of habit!!!"

debugging is still ugly but at least the different browsers can SEE the errors
(pp.313-315 how to "turn on" the reporting in browser you are using & experiment)
control-shift-j for Firefox
Will only show JavaScript problems. No help at all with PHP issues.

Arrays use square brackets!

topRow    = ['red', 'green', 'blue'  ]; 
middleRow = ['cat', 'rat'  , 'donkey']; 
bottomRow = [  1  ,    2   ,    3    ];

silly = [ topRow, middleRow, bottomRow ];

operators same as for PHP except CONCATENATION which is a PLUS SIGN

Variables and Scoping

global variables
- every part of script has access to read or change
- defined outside any function (with/without keyword var) OR inside a function without keyword var
local variables
- only exist for the one function where it appears
- defined INSIDE a function and WITH keyword var
function parameters same as local EXCEPT for ARRAYS
(Ask me what "pass by reference" means...)

var, var, var! what a mess! tias ... what will be printed?

                    <script>
                          x="oh, good grief!";  // x has global scope
                          var y="why is that?"; // y has global scope
                          z = testMyPatience(); // z has global scope
                                                //        because...all outside any fcn. period.  

                          document.write("       x is "+x);
                          document.write("<br>y is "+y);
                          document.write("<br>z is "+z);

                          document.write(" <p>a is "+a);
                          document.write("<br>b is "+b);
                          document.write("<br>c is "+c);

                          function testMyPatience(){

                             a=123;             // a has global scope
                                                //        because...INSIDE a fcn & NO keyword 'var'

                             var b=123;         // local scope
                                                //        because...INSIDE a fcn & keyword 'var'

                             if (a == 123){ 
                               var c=723;       // local scope
                                                //        because...INSIDE a fcn & keyword 'var'
                             }

                             return "whatever";
                          }
                    </script>

document.write()
Dr Dale says "DO NOT USE
document.write(...);
IN FUTURE (There will be a better way that uses .innerHTML!)

DOM, Here's another image