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What is TypeScript? A Beginner's Guide

JavaScript is considered a weakly typed language. In this lesson, we'll go through a simple example of why that can be an issue in development and where TypeScript falls in the picture.

Introducing TypeScript

📝 This lesson's quiz can be found - here.
🗒️ Solutions for this lesson's quiz can be found - here.

JavaScript is considered a weakly typed language which means that in JavaScript, we have the ability to assign one data type to a variable and later on assign another data type to that same variable.

Let's see an example of this in our index.js file. We'll look to replicate what we've done before by creating two variables, one and two, and attempt to show the summation of these two variables.

In the src/index.js of our server project, we'll create constant variables labeled one and two and provide numerical values of 1 and 2 respectively.

const one = 1;
const two = 2;

In the callback function of our app.get() method for the index route, we'll send an interpolated string that says 1 plus 2 is equal to the sum of the variables one and two.

app.get("/", (req, res) => res.send(`1 + 2 = ${one + two}`));

When we launch our app in http://localhost:9000/, we'll see an output of 1 + 2 = 3.

What if shortly after we've instantiated our constant variables, we decide to reassign the two variable to be a string with a value of 'two'. Since we're reassigning the value of a variable - we'll change how we instantiate the variable by using the let keyword.

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