A Deeper look into Javascript Basics

A deeper look
into
Presentation By :
Ashutosh Mahto
Mindfire Solutions
Javascript Basics

“The world's most misunderstood programming language”
- Douglas Crockford
A Deeper Look Into Javascript Basics

Agenda to Discuss
Hoisting in javascript
Scopes In javascript
Objects
Functions
Closures
Prototype
Drawing some basic practices

Hoisting in Javascript
Every declaration, variable declaration or function declaration is hoisted to
the top of its declaration context.
/* Hoisiting */
var name = "ramesh";
function showName() {
if (!name) {
var name = "Suresh";
}
console.log(name);
}
showName(); // output - Suresh

Defining Scopes in Javascript
- Everything defined without var is global
- Every global variable or object can be accessed through
window.<variablename>
- Unlike C, Javascript doesn't have Block Level Scope
- Javascript has Function Level Scope

Defining Scopes in Javascript
#include <stdio.h>
int main() {
int x = 1;
printf("%d, ", x); // 1
if (1) {
int x = 2;
printf("%d, ", x); // 2
}
printf("%dn", x); // 1
}
var x = 1;
console.log(x); // 1
if (true) {
var x = 2;
console.log(x); // 2
}
console.log(x); ???
Output – 2, which should be 1 as
in C
Scope in C Scope in Javascript

Object In Javascript
- Everything except Number, String, Boolean, null and undefined
are objects.
- Can be created using object literals or through Object constructor.
- Objects are usually key value pairs.
- Objects can be used as Associative Arrays, but are not actually
any type of array.
- Objects can link to another objects through -
var newObject = Object(oldObject);
This will create a new object and keep a link to the Old Object.
If any property is not available in newObject it will be looked into
oldObject

Functions In Javascript
- Executable piece of code, in any programming language.
- In javascript, functions are INVOKABLE objects.
- Like objects functions can carry Properties & Methods, can be
copied, deleted and augmented
- Functions can be passed as parameter to other functions and can
be returned also
- Functions are First Class Citizens in javascript.
- Every function returns a value, if not, returns undefined.

Functions in Javascript
- Function declaration
function sayHello() {
console.log('Hello!');
}
- Function expression
var sayHello = function() {
}
- Anonymous Functions
- Self executing functions
(function() {
})();

Closures in Javascript
Local variables for a function are kept alive after the function has
returned
A closure is a stack-frame which is not deallocated when the function
returns (as if a 'stack-frame' were malloc'ed instead of being on the
stack!)
var greet = function(time) {
var good = "Good";
return function(name){
console.log(good+ " "+ time+ " "+ name);
}
}
var sayGoodMorning = greet("Morning");
sayGoodMorning("Suresh");
// Good Morning Suresh

Prototype in Javascript
Prototype is the base of Object Oriented Programming in javascript
Every function contains a prototype object that can be chained
through its constructor.
var Person= function(name) {
this.name = name;
}
Person.prototype.getName = function() {
return this.name;
}
var student = new Person("Satish");

Drawing some best practices
Start using JSLint
Start using “strict”
Always use var while declaring variables to avoid unnecessary globals
Declare all the variables at the top of its function scope
Maximize the use of function expressions
Always use ; as delimiter
Never think of Objects as a kind of array, and never declare an object
as an array.

Any Question ???

References and Recommendations

Books
− JavascriptThe Good Parts, Douglas Crockford
− Javascript:The Definitive Guide, David Flanagan
− Professional Javascript For Developers, Nicholas Zakas

Blogs

Articles

Stack Overflow

ThankYou !!!

A Deeper look into Javascript Basics

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