kirthi2005 / closure

Closure defnition and an example. Thanks to Dave Gray!

Closure

Defnition: "A closure is a function having access to the parent scope even after the parent function has closed"

Example:

let x = 1; //global scope
const parentFunction = () => {
    //parent scope 
    let y = 2;
    console.log(x);
    console.log(y);
    const childFunction = () => {
        //local scope
        console.log(x += 5);
        console.log(y += 1);  
    }
    return childFunction;
}
const result = parentFunction();
console.log(result); 
result(); /* calling child function. it will access y in parent function 
even the parent function has already been called and closed. child function 
still has access to the scope and that makes y private variable that
only child function has access to */

Output:

  1
  2
  ()=>{
    //local scope
        console.log(x += 5);
        console.log(y += 1);
  }
  6
  3

Points to Remember:

- controls the variable that are being shared with the nested function
- the inner function has access to the variables in its local scope, parent function and in the global scope 
- In Js, we can use private variables and methods using closure
- helps in maintaining the state between each function calls without using a global variable.
- closure is created at function definition not at function invocation.