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May 23, 2018 JavaScript has always allowed you to work with key/value pairs through objects. The Maps collection made available with ES6 improves on that. In this tutorial we cover Maps. Getting value out of maps that are treated like collections is always something I have to remind myself how to do properly. In this post I look at JavaScript object iteration and picking out values from a JavaScript object by property name or index.
- Generate Key Map Object Javascript Free
- Get Keys Javascript Object
- Javascript Get Keys
- Generate Key Map Object Javascript Pdf
- Map In Javascript
- Map Key Definition
- Key Map Houston
Real Life Objects, Properties, and Methods
In real life, a car is an object.
A car has properties like weight and color, and methods like start and stop:
Object | Properties | Methods |
---|---|---|
car.name = Fiat car.model = 500 car.weight = 850kg car.color = white | car.start() car.drive() car.brake() car.stop() |
All cars have the same properties, but the property values differ from car to car.
All cars have the same methods, but the methods are performed at different times.
JavaScript Objects
You have already learned that JavaScript variables are containers for data values.
This code assigns a simple value (Fiat) to a variable named car:
Objects are variables too. But objects can contain many values.
This code assigns many values (Fiat, 500, white) to a variable named car:
var car = {type:'Fiat', model:'500', color:'white'};
Try it Yourself »The values are written as name:value pairs (name and value separated by a colon).
JavaScript objects are containers for named values called properties or methods.
Object Definition
You define (and create) a JavaScript object with an object literal:
Generate Key Map Object Javascript Free
Example
var person = {firstName:'John', lastName:'Doe', age:50, eyeColor:'blue'};
Try it Yourself »Spaces and line breaks are not important. An object definition can span multiple lines:
Example
var person = {
firstName: 'John',
lastName: 'Doe',
age: 50,
eyeColor: 'blue'
};
Try it Yourself »firstName: 'John',
lastName: 'Doe',
age: 50,
eyeColor: 'blue'
};
Object Properties
The name:values pairs in JavaScript objects are called properties:
Property | Property Value |
---|---|
firstName | John |
lastName | Doe |
age | 50 |
eyeColor | blue |
Accessing Object Properties
Get Keys Javascript Object
You can access object properties in two ways:
or
Example1
Try it Yourself »Example2
Try it Yourself »Object Methods
Objects can also have methods.
Methods are actions that can be performed on objects.
Methods are stored in properties as function definitions.
Property | Property Value |
---|---|
firstName | John |
lastName | Doe |
age | 50 |
eyeColor | blue |
fullName | function() {return this.firstName + ' ' + this.lastName;} |
Javascript Get Keys
A method is a function stored as a property.
Example
var person = {
firstName: 'John',
lastName : 'Doe',
id : 5566,
fullName : function() {
return this.firstName + ' ' + this.lastName;
}
};
firstName: 'John',
lastName : 'Doe',
id : 5566,
fullName : function() {
return this.firstName + ' ' + this.lastName;
}
};
The this Keyword
In a function definition,
this
refers to the 'owner' of the function.In the example above,
this
is the person object that 'owns' the fullName
function.In other words,
this.firstName
means the firstName
property of this object.Generate Key Map Object Javascript Pdf
Read more about the
this
keyword at JS this Keyword.Accessing Object Methods
You access an object method with the following syntax:
Example
Try it Yourself »If you access a method without the () parentheses, it will return the function definition:
Example
Try it Yourself »Do Not Declare Strings, Numbers, and Booleans as Objects!
When a JavaScript variable is declared with the keyword '
new
', the variable is created as an object: Map In Javascript
var x = new String(); // Declares x as a String object
var y = new Number(); // Declares y as a Number object
var z = new Boolean(); // Declares z as a Boolean object
var y = new Number(); // Declares y as a Number object
var z = new Boolean(); // Declares z as a Boolean object
Map Key Definition
Avoid
String
, Number
, and Boolean
objects. They complicate your code and slow down execution speed.Key Map Houston
You will learn more about objects later in this tutorial.