The simple types of javascript are : numbers , booleans , strings , null and undefined. All other types are objects in javascript. Hence a detailed knowledge is required for manipulating objects in javascript. Remember : Objects in javascript are class free. They are basically name value pairs surrounded by curly braces.Objects are always passed around by reference.
Initialization :
Retireval :
For filling in default values for undefined objects use the '||' operator.Attempting to retrieve values from undefined will throw a TypeError exception.
Updation :
Updation can be done by the assignment operator. If the object does not have the property name then it is augmented to the property names present with the value that is assigned.
Prototype :
Every object in javascript inherits properties from some other object. All objects created directly inherit from the Object.prototype an object that comes along with javascript.
If we try to retrieve a value from an object and that property is not present javascript tries to retrieve the property from the obejcts prototype and then from the prototype of the prototype and so on till it reaches the Object.prototype. If it is found nowhere in the chain then it is undefined.This is called delegation in javascript.
A detailed description on Prototype will be provided in the next few platters of inheritance in javascript.However for now we can use Object.create function which takes a prototype from which to derive the new Object. One can also assign the protoype property with an object . i.e.
The difference between the two is that in Object.create the constructor is not called hence the object remains uninitialized.
If we add a new property to the prototype then the new property will show in each object derived from that prototype.
But then how do we know whether the property belongs to the object or to the prototype chain.This can be known by using the hasOwnProperty which does not look into the property chain.For example:
Enumeration :
For enumerating the properties of the object use the for in construct .This includes the prototype chain properties.Hence we need to filter using typeof and hasOwnProperty. Careful Note :: The elements can come in any order.
Deletion : The delete operator can be used to remove a property from object. Deleting may allow the prototype property to be accessible.
Initialization :
var empty_object = {};
var exobj = {
'name':'saswat',
'occupation':'student'
};
Retireval :
exobj['name'] //returns 'saswat'
exobj.name //preferred and more cleaner
exobj.status // not present hence returns undefined
For filling in default values for undefined objects use the '||' operator.Attempting to retrieve values from undefined will throw a TypeError exception.
Updation :
Updation can be done by the assignment operator. If the object does not have the property name then it is augmented to the property names present with the value that is assigned.
Prototype :
Every object in javascript inherits properties from some other object. All objects created directly inherit from the Object.prototype an object that comes along with javascript.
If we try to retrieve a value from an object and that property is not present javascript tries to retrieve the property from the obejcts prototype and then from the prototype of the prototype and so on till it reaches the Object.prototype. If it is found nowhere in the chain then it is undefined.This is called delegation in javascript.
A detailed description on Prototype will be provided in the next few platters of inheritance in javascript.However for now we can use Object.create function which takes a prototype from which to derive the new Object. One can also assign the protoype property with an object . i.e.
exobj.prototype = new User() ; //user as prototype object
exobj.prototype = Object.create(User.prototype);
The difference between the two is that in Object.create the constructor is not called hence the object remains uninitialized.
If we add a new property to the prototype then the new property will show in each object derived from that prototype.
But then how do we know whether the property belongs to the object or to the prototype chain.This can be known by using the hasOwnProperty which does not look into the property chain.For example:
exobj.hasOwnProperty('name') //true
exobj.hasOwnProperty('constructor') //false
Enumeration :
For enumerating the properties of the object use the for in construct .This includes the prototype chain properties.Hence we need to filter using typeof and hasOwnProperty. Careful Note :: The elements can come in any order.
for ( property in exobj ){
if( exobj.hasOwnProperty(property) && typeof exobj[property] == 'string')
//do something
}
Deletion : The delete operator can be used to remove a property from object. Deleting may allow the prototype property to be accessible.
