Mastering TypeScript 3 - Third Edition

JavaScript closures

Before we continue with this chapter, let's take a quick look at how TypeScript implements classes in the generated ES3 or ES5 JavaScript through a technique called closures. As we mentioned in Chapter 1, TypeScript – Tools and Framework Options, a closure is a function that refers to independent variables. These variables essentially remember the environment in which they were created. Consider the following JavaScript code:

function TestClosure(value) { 
    this._value = value; 
    function printValue() { 
        console.log(this._value); 
    } 
    return printValue; 
} 
 
var myClosure = TestClosure(12); 
myClosure; 

Here, we have a function named TestClosure that takes a single parameter, named value. The body of the function first assigns the ...