TypeScript typing

TypeScript, on the other hand, is a strongly typed language. Once you have declared a variable to be of a certain type, you cannot change it. As an example, if you declare a variable to be of type string, then you can only assign string values to it, and any instance of this variable can only treat it as though it has a type of string. This helps to ensure that code that we write will behave as expected. When we know immediately that the value of a variable will always be a string, we will know which of these conversion rules JavaScript will use.

JavaScript programmers have always relied heavily on documentation to understand how to call functions, and the order and type of the correct function parameters. But what if we could take all of this documentation and include it within the IDE?

Then, as we write our code, our compiler could point out to us—automatically—that we were using variables or functions in a JavaScript library in the wrong way. Surely this would make us more efficient, more productive programmers, and allow us to generate better code with fewer errors?

TypeScript does exactly that. It introduces a very simple syntax to define the type of a variable in order to ensure that we are using it in the correct manner. If we break any of these rules, the TypeScript compiler will automatically generate errors, pointing us to the lines of code that are in error.

This is how TypeScript got its name. It is JavaScript with strong typing, hence TypeScript. Let's take a look at this very simple language syntax that enables the Type in TypeScript.