Identifiers by George Hernandez

var
label: statement
this
typeof
with
Reserved Words
Intrinsic Properties

var

The var statement declares variables, and optionally initializes them.

var variable [ = value ] [, variable2 [ = value2], ...]

When a object or variable is explicitely declared with var, its value may optionally be initialized.
There are general two scopes in JS: function scope and application/global scope. Looping statements such as for or while look like "functions" and their counters are often declared within their parentheses, (EG: var i = 0) but those variables are not local to the loop, but rather are in the same scope as the loop statement.
If a variable is initialized without an explicit declaration (i.e. without var), then it is implicitly declared automatically and assumes the scope it was written in. There is no JavaScript equivalent to "Option Explicit" which forces explicit declarations.
One practice is always explictly declare variables at the top of the application or at the top of each function.
JavaScript variables are loosely typed, meaning that the data type can change under different circumstances.
The first character of must be a letter (a-z or A- Z), an underscore (_), or a dollar sign ($). As of JS 1.5 you can also use any Unicode letter or Unicode escape sequence (\uXXXX).
The other characters can also include numbers (0-9).
Identifiers must not be a reserved word.
JavaScript is case sensitive!

label: statement

Indicates that starting point of a statement block.

labelName: statements

this

this.property

Refers to the current object and is commonly used when setting multiple properties. EG:

function Car(color, make, model) {
    this.color = color;
    this.make = make;
    this.model = model;
}

Another common usage is to pass the current form to a function. EG:

<input type="button" value="Run" onClick="RunMe(this.form)">

typeof

typeof expression
typeof (expression)

Returns string indicating the type in JS. The 6 types in JS are as follows.

string. EG: typeof 'hi';
number. This includes the following.
- integer.
  - decimal. EGs: -2, -1, 0, 1, 2, ... 8, 9, 10, 11.
  - octal. EGs: 00, 01, ... 07, 010, 011.
  - hexadecimals. EGs: 0x0, 0X1, ..., 0x9, 0XA, 0xb, ...0xF, 0x10, 0x11.
- floating points. EGs: -12e3, 1.3E2, 2.7e-4.
boolean. true or false.
object. EG: typeof null;
function. EGs:
- var f=new Function(); typeof f; //function
- var g=new Function('return 7'); typeof f; //number
undefined. EGs:
- var x='x'; typeof x; //string
- y; typeof y; //undefined
- typeof z; //undefined
- typeof void(0); //undefined
- var g=new Function(void(0)); typeof g(); //undefined
- var h=new Function(); typeof h(); //undefined

There are some particular about applying typeof on different global objects or functions. EGs:

typeof Math //object
typeof Date //function
typeof Function //function
typeof Object //function
typeof String //function

with

with (object) {
  statement;
}

Establishes the default object for the statement. Assumes that each variable in the statement is a property/object of the default object.

The following table lists reserved words that cannot be used as JavaScript variables, member names, function parameters, or statement labels. Oddly enough, only the ones in bold below are even used by JavaScript, the rest are reserved according to the ECMAScript specifications.

abstract boolean break byte case catch char class const continue debugger default delete do double	else enum export extends false final finally float for function goto if implements import in	instanceof int interface long native new null package private protected public return short static super	switch synchronized this throw throws transient true try typeof var void volatile while with

Intrinsic Properties

These are top level properties that are neither user defined variables or properties associated with objects.

infinity. The value of this infinity is always greater than any number including itself.
NaN. Not-a-Number. The value of this NaN is always not equal to any number including itself.
undefined. The value and type of a variable if it has not been defined yet.

Page Modified: (Hand noted: 2003-05-15 00:00:00Z) (Auto noted: 2008-10-16 21:19:56Z)

Identifiers

var

label: statement

this

typeof

with

Reserved Words

Intrinsic Properties