Skip to main content

JavaScript Closure

What is closure?

It is my personal experience, I have never understood closure, I have read many articles & have seen many videos. Finally, I understood sometimes we even used a closure without realizing we were using a closure.
First, understand the meaning of closure “an act or process of closing something”, now we can relate closure in javascript, closure is an inner function which wraps inside the outer function, which can access outer function scope & global function scope. for scoping you can read my previous blog:- http://uisource.blogspot.com/2018/08/javascript-variable-scoping.html

why do we create?

Global variables can be made local (private) with closures.
To avoid the usage of global variables, use the local variables and wrap your code in the closure.
A closure is an inner function that has access to the outer (enclosing) function’s variables—scope chain(Lexical scoping).
The closure has three scope chains: it has access to its own scope (variables defined between its curly brackets), it has access to the outer function’s variables, and it has access to the global variables.
A closure is a function having access to the parent scope, even after the parent function has closed.
Example
 function outerFunc(){
        var msg ="hello i am outer function variable"
        function innerFunc(){
            console.log(msg);
        }
        return innerFunc;
    }
    var y = outerFunc();
    console.log(y)        // output ƒ innerFunc(){ console.log(msg);}
    y();   // hello i am outer function variable





The reference to the inner innerFunc(…) function that gets returned with
each call to the outer outerFunc(…) is able to remember whatever msg
value inside outerFunc(…).
A closure is not only created when you return an inner function. In fact, the enclosing function does not need to return at all in order for its closure to be created. 

Comments

Post a Comment

Popular

JavaScript type hoisting with variable function Expression

JavaScript type hoisting with variable function Expression Hoisting is JavaScript default behavior to moving declaration on the top. Variable can be used before its declaration. To understand this, first we need to understand of hoist meaning, hoist means “raise(something) by means of ropes & pulleys”. now we can relate hoisting with JavaScript. JavaScript interpreter moves all declaration on the top at runtime. It is best practice to declare all variable at the top of their respective scopes. , JavaScript is loosely syntax language so it will not throw any error at runtime if the variable used before its declaration. But JavaScript does not allow variable used before its declaration in “use strict” mode. Example 1 In this example, we can see in a normal scenario, when y has declared & then used. in this case, it will give output 10 as excepted. <p id= "demo" ></p> <script> var y; //Declare y y = 10 ; ...
4 comments
Read more

JavaScript Variable Scoping

There are two types of variables in JavaScript.  Global variables have global access and are declared outside of any function. Local variables are those declared inside of function. Lexical Scoping(Nested JavaScript Function) means that in a nested group of functions, the inner functions have access to the variables and other resources of their parent scope. Global variable:- Global variable declares & initialize outside the function, & accessible in from anywhere in the code. The global variable always stored in memory even function execution finish, it always keeps in memory or always accessible from anywhere in the code. Example 1 var message= "hello i am global variable" ; //global variable function a (){ console.log(message); // output: hello i am global variable } function b (){ console.log(message); // output: hello i am global variable } function a() function b() In above example message is a global variab...
1 comment
Read more