JavaScript Pain Points: Runtime Bugs

In this lesson we explore the runtime bugs that motivated TypeScript's creation. JavaScript is flexible — but that flexibility can cause hard-to-find errors.

JavaScript silently coerces types. Adding a number to a string returns a string, not an error. This causes unexpected behavior at runtime.

// JavaScript
let total = 5 + '10'; // '510' not 15
console.log(total);   // '510'