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The answer is that you can’t learn TypeScript without learning JavaScript! We frequently see the question “Should I learn JavaScript or TypeScript?“. Your programs will use the same standard library (or external libraries) as JavaScript programs, so there’s no additional TypeScript-specific framework to learn. The bottom line is that while you might see type errors during compilation, the type system itself has no bearing on how your program works when it runs.įinally, TypeScript doesn’t provide any additional runtime libraries. This also means that TypeScript never changes the behavior of your program based on the types it inferred.

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This means that once your code is compiled, the resulting plain JS code has no type information. Roughly speaking, once TypeScript’s compiler is done with checking your code, it erases the types to produce the resulting “compiled” code. Keeping the same runtime behavior as JavaScript is a foundational promise of TypeScript because it means you can easily transition between the two languages without worrying about subtle differences that might make your program stop working. This means that if you move code from JavaScript to TypeScript, it is guaranteed to run the same way, even if TypeScript thinks that the code has type errors. TypeScript is also a programming language that preserves the runtime behavior of JavaScript.įor example, dividing by zero in JavaScript produces Infinity instead of throwing a runtime exception.Īs a principle, TypeScript never changes the runtime behavior of JavaScript code.

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Throughout this guide we’ll demonstrate how to add various TypeScript syntax to eliminate such errors. These may be legitimate problems with the code, or TypeScript being overly conservative. If you move some code from a JavaScript file to a TypeScript file, you might see type errors depending on how the code is written. (Later, we’ll learn about settings you can use to configure how strictly TypeScript checks your code.) TypeScript’s type checker is designed to allow correct programs through while still catching as many common errors as possible. It’s possible you really did intend to divide a number by an array, perhaps just to see what happens, but most of the time, though, this is a programming mistake. 2363 The right-hand side of an arithmetic operation must be of type 'any', 'number', 'bigint' or an enum type. log ( 4 / ) The right-hand side of an arithmetic operation must be of type 'any', 'number', 'bigint' or an enum type. JavaScript’s equality operator ( =) coerces its arguments, leading to unexpected behavior:Ĭonsole. To summarize, we have a language that was designed for quick uses, and then grew to a full-fledged tool to write applications with millions of lines.Įvery language has its own quirks - oddities and surprises, and JavaScript’s humble beginning makes it have many of these. There are many developers these days that use only JavaScript to program their entire stack! The “run anywhere” nature of JS makes it an attractive choice for cross-platform development. More than this, JS has become popular enough to be used outside the context of browsers, such as implementing JS servers using node.js. This is long and gradual growth of “the web”, starting as a simple network of static pages, and evolving into a platform for rich applications of all kinds. On modern websites, your browser is frequently running applications that span hundreds of thousands of lines of code. Web browser developers responded to this increased JS usage by optimizing their execution engines (dynamic compilation) and extending what could be done with it (adding APIs), which in turn made web developers use it even more.

Over time, though, JS became more and more popular, and web developers started using it to create interactive experiences. JavaScript (also known as ECMAScript) started its life as a simple scripting language for browsers.Īt the time it was invented, it was expected to be used for short snippets of code embedded in a web page - writing more than a few dozen lines of code would have been somewhat unusual.ĭue to this, early web browsers executed such code pretty slowly. The relationship between TypeScript (TS) and JavaScript (JS) is rather unique among modern programming languages, so learning more about this relationship will help you understand how TypeScript adds to JavaScript. You’ve probably already heard that TypeScript is a “flavor” or “variant” of JavaScript. Congratulations on choosing TypeScript as one of your first languages - you’re already making good decisions!

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