Javascript, Grammar, Objects and Methods « »

Contents

• Gramar
• Objects
  • Object Literals
  • Retrieval
  • Default Values
  • Reference
  • Prototype
  • Delegation
  • Reflection
  • hasOwnProperty
  • Enumeration
  • Delete
  • Global Abatement
• Methods
  • Array
  • Function
  • Number
  • Object
  • RegExp
  • String

Javascript has a malleable nature and lack of type checking.

We use javascript for things like:

• User Interface (UI) manipulation
• Client Server interaction
• Business processing/validation

Gramar

• Whitespace
• Names
• Numbers
• Strings
• Statements
  • Falsy values
    • false
    • null
    • undefined
    • empty string ‘’
    • number 0
    • number NaN
  • switch
  • case
  • while
  • for
  • do
  • try
  • throw
  • return
  • break
• expression
  • precedence
    • . [] ()
    • delete new typeof + - !
    • / %
    • + -
    • >= <= > <
    • === !==
    • &&
    • ||
    • ?:

Objects

The simple types of Javascript are

• numbers
• strings
• booleans
• null
• undefined
• objects

Javascript includes a prototype linkage feature that allows one object to inherit the properties of another.

Object Literals

var empty_object = {};

var stooge = {
	"first-name": "Jerome",
	"last-name": "Howard"
};

var flight = {
	airline: "Oceanic",
	number: 815,
	departure: {
		IATA: "SYD",
		time: "2004-09-22 14:55",
		city: "Sydney"
	},
	arrival: {
		IATA: "LAX",
		time: "2004-09-23 10:42",
		city: "Los Angeles"
	}
};

Retrieval

//Both ways are correct but the second one is preferred
var var1 = stooge['first-name'];
var var2 = flight.deaprture.IATA;

Default Values

var status = flight.status || "unknown";

Attempting to retrieve values from undefined will trhow a TypeError exception.

Reference

Objects are passed around by reference. They are never copied.

Prototype

Every object is linked to a prototype object from which it can inherit properties. All objects created from object literals are linked to Object.prototype, an object that comes standard with JavaScript.

Delegation

The prototype link is used only in retrieval. If we try to retrieve a property value from an object, and if the object lacks the property name, then JavaScript attempts to retrieve the property value from the prototype object. This is called delegation.

Reflection

Usually it’s very helpfu to use typeof. But scare must be taken because any property on the prototype chain can produce a value.

hasOwnProperty

It returns true if the object has a particular property. The hasOwnProperty does not look at the prototype chain.

myObject.hasOwnProperty('propertyName');

Enumeration

The for in statement can loop over all of the property names in an object. The enumeration will include all of the properties including functions and prototype properties. If you want to filter out these values you have to use the hasOwnProperty.

var propertyName;
for(propertyName in myObject){
	if(typeof myObject[propertyName] !== 'function' && myObject.hasOwnProperty(propertyName)){
		document.writeln(name + ': ' + myObject[propertyName]);	
	}
	
}

If we want a specific order whe need an array.

var i;
var properties = [
	'first-name',
	'middle-name',
	'last-name',
	'profession'
];
for(i = 0; i < properties.length; i +=1 ){
	document.writeln(properties[i] + ': ' myObject[properties[i]]);
}

Delete

The delete operator can be used to remove a property from an object.

Removing a property from an object may allow a property from the prototype linkage to shine through.

delete myObject.propertyOne;

Global Abatement

One way to minimize the use of global bariables is to create a single global variable for your application:

var MYAPP = {};

Methods

Array

Go to the arrays post

Function

• function.apply(thisArg,argArray)

Number

• number.toExponential(fractionDigits)
• number.toFixed(fractionDigits)
• number.toPrecision(precision)
• number.toString(radix)

Object

• object.hasOwnProperty(name)

RegExp

• regexp.exec(string)
• regexp.test(string)

String

• string.charAt(pos)
• string.charCodeAt(pos)
• string.concat(string…)
• string.indexOf(searchString, position)
• string.lastIndexOf(searchString, position)
• string.localeCompare(that)
• string.match(regexp)
• string.replace(searchValue, replaceValue)
• string.search(regexp)
• string.slice(start,end)
• string.split(separator,limit)
• string.substring(start,end)
• string.toLocaleLowerCase()
• string.toLocaleUpperCase()
• string.toLowerCase()
• string.toUpperCase()
• String.fromCharCode(char…)