MEAN Web Development - Second Edition

JavaScript Closures

Closures are functions that refer to variables from their parent environment. To understand them better, let's take a look at the following example:

function parent() {
    const message = 'Hello World';

    function child() { 
        alert (message);
    }

    child(); 
}

parent();

In the preceding example, you can see how the child() function has access to a constant defined in the parent() function. However, this is a simple example, so let's look at a more interesting one:

function parent() {
   const message = 'Hello World'; 
    
    function child() { 
    alert (message); 
  }

   return child;
}

const childFN = parent();
childFN();

This time, the parent() function returned the child() function, and the child() function is called after the parent() function has already ...