Understanding TypeScript’s Most Common Type Errors
Get comfortable with the compiler’s most common complaints and learn how to fix them with clarity and confidence.
Every developer runs into a problem: you write what seems like perfectly reasonable code, and TypeScript shows an error. The error is red, the tooltip is long, and the compiler isn’t letting you move on.
Good.
This is exactly where we level up. In this lesson, we’re going to get inside the mind of the TypeScript compiler. Understand what it’s telling us, why it’s panicking, and how we can respond intelligently without reaching for any.
Let’s get comfortable with the most common types of errors and learn how to turn them into learning opportunities.
“Type ‘X’ is not assignable to type ‘Y’”
This is a typical TypeScript error and one you’ll see a lot. It means we tried to assign a value that doesn’t match the expected type.
let count: number = 10;count = "ten"; // ❌console.log(`Count: ${count}`);
In line 2, the compiler expected a number, but got a string. Even though "ten" might look like a number in disguise, it’s a string, and TS isn’t playing pretend.
This error almost always means one of two things:
You’ve got the wrong value.
You’ve got the wrong type annotation.
To fix it, refactor one or the other. But don’t ignore the message—it’s doing its job.
If the type annotation is ...