Javascript summary -mycode.coolpage.biz

Javascript

Javascript is a dynamic and lightweight programming language common used as part of web pages. It is different from java

Development tools

Microsoft Front Page
Micromedia DreamWeaver MX

Javascript is case sensitive

Comments

Singleline: Any text after // and before end of line.
Multiline: Any text between /* and */

Placement

Javascript code can be placed anywhere in html document e.g body,head etc

	 <script type="text/javascript">
JavaScript code
</script>

Javascript from external source

	 <script type="text/javascript" src="http://www.example.com/file.js"></script>
	 or
	 <script type="text/javascript" src="file:///sdcard/file.js"></script>

Statements

Javascript statements are separated by semi-colons
Javascript ignores whitespaces. Use them to format your code

	 var a = 5; //a statement
	 alert(a*a); // another statement

Output

To provide visible data to user javascript uses:

alert(text/variable)
console.log(text/variable)
document.write(text/variable)
element.innerHTML=text/variable
element.value=text/valuable

Variables

They are used to temporarily store data

	 var a = 5; //Number
	 var b= "Titus";  //String
	 var c = true;  //Boolean
	 var d= ["Joy","James"];  //Array
	 var e ={firstName:"John",lastName:"Kamau"}; //Object
	 var f=new Function(params);  //Function

Rules

Must begin with a letter,underscore or dollar sign
Case sensitive and unique

Scope

Global:- Outside Functions
Local:- Inside functions
without a var keyword the variable is a property of the global object.

Operators

Arithmetic

+ Addition
- Subtraction
* Multiplication
/ Division
% Modulus
++ Increment
-- Decrement

Comparison

== Equal to
=== Equal value
!= Not equal
!== Not equal value and type
> Greater than
< Less than
>= Greater or equal to
<= Less or equal to
? Ternary/Conditional operator

String

+ Combine two strings
+= Add more strings to a variable

Assignment

Logical

&& And
|| Or
! Not

Bitwise

& AND
| OR=
~ NOT
^ XOR
<< Left Shift
>> Right Shift

Others

typeof(variable): returns the data type
delete: Deletes a property from object
in: Checks a property in object
instanceof:
void: No return

Data types

Strings: "Titus"
Numbers: 5
Arrays: []
Booleans: true or false
Objects: {}
Functions: function(){ }

Functions

Function is a block of code that perform a particular function. It is executed when invoked.A function is reusable and is accesible from any part of a program

    function multiply(p1,p2){
    return p1*p2;
    }

Coditional Statements

To write a code that thinks you have to put conditions
Condition is a statement that returns positive or negative data type
Examples of negative data types are

"" (string)
0 (Number)
false (boolean)
null (Object)
undefined
NaN

if

    if(condition){
    code block executed if condition is pisitive
    }

if...else

    if(condition){
    code block executed if condition is positive
    }
    else{
    code block executed if condition is negative
    }

if...else if...else

    if(condition){
    code block executed if condition is positive
    }
    else if(condition2){
    code block executed if condition2 is positive
    }
    else{
    code block executed if condition is negative
    }

Switch

switch is a more simpler version of if..else if..else

    switch(data){
    case condition: code block executed if condition is equal to data; break;
    case condition2: code block executed if condition2 is equal to data; break;
    default: code block executed if all conditions are not met;
    }

Loops

Loop is piece of code is executed many times repeatedly

for

    for(initialization;condition;interation){
    code block
    }
    // initialization: initialise a variable e.g i=0
    //condition : set a condition e.g i<10
    //intelation : increment or decrement e.g i++,i--,i=i+2

for/in

It loops through properties in an object

    for(property in object){
    code block
    }
    //example
    for(x in window){
    document.write(x);
    }

while

You have to satisfy condition from within the code block.

    while(condition){
    code block
    }
    //example
    while(i<10){
    document.write(i);
    i++
    }

do.. .while

Checks condition after code execution

    do{
    code block;
    }
    while(condition)

break is used to jump out of loop
continue break one interation with a condition and continues to the next

Conversions

To String: String(variable)
To Number: Number(variable)
To Float: parseFloat( variable)
To Interger: parseInt(variable,base)
To Array: new Array(variables)
To Object: new Object(variables)
To new Function: new Function(variables)

Regular expressions

It is a sequence of characters that form a search pattern

    /pattern/modifiers

modifiers

i: case insensitive
g: global

String methods used

match()
search()
replace()

Handling errors

try...catch

    try{
    block of code expected to have error.
    }
    catch(error){
    block of code executed after an error occur.
    }
    finally{
    block of code executed whether there was error or not.
    }

onerror(DOM)

    onerror= function(error){ handle error}

Global methods

decodeURI()
decodeURI()Component
encodeURI()
encodeURIComponent()
escape()
unescape
eval(expression): evaluates an expession/block of code/function/string etc
isNaN: checks whether a variable is a number
isFinite(number): checks whether number has reached infinity
parseInt(number): converts to interger
parseFloat(number): converts to float

JSON

Javascript Object Notation

    {
    "action":"android.intent.action.VIEW",
    "type" : "message/rfc822",
     "data":"/sdcard/hd.jpg",
    "extras" : {name:"android.intent.extra.EMAIL", type:"list", value:"yourname@gmail.com"}
   }

JSON methods

JSON.stringify(object) Converts object to JSON
JSON.parse(JSON) Converts JSON to Object

Rules

data is in quotes
Array is inside []
Object is inside {}

Best Practices

Initialize your variables with var keyword
- Slow code: for(i=0;i<array.length;i++){}
- Fast code: var len = array.length; for(i=0;i<len;i++){}
End statements with a semi-colon. Not a must when each statement is on its own line
Dont use reserved words as variable names