Avoiding data type conversion in JavaScript/TypeScript

Currently delving into the world of JavaScript, I come from a background of working with statically typed languages. Naturally, I opted to dive into TypeScript instead of starting directly with JS. While TypeScript is great and addresses many issues present in JS, the concept of "weak typing" really bothers me.

It just doesn't sit right with me that I can do something like this:

let int: number = 42
let str: string = "69"

console.log(int + str)

Is there a way in TypeScript to prevent these type conversions from happening? I would prefer to receive an error when trying to add a string to an integer.

javascripttypescriptcasting

Answer №1

There is no strict rule in TypeScript that would prohibit you from performing the operation; when you add an integer and a string together, the result will be of type string.

However, if you attempt to save this result in a variable declared as type number, it will generate an error:

let int: number = 42
let str: string = "69"

let result: number = int + str;
//  ^ error: Type 'string' is not assignable to type 'number'.(2322)

This behavior is not exclusive to loosely-typed languages; even strongly-typed languages like Java and C# exhibit similar behavior, automatically converting numbers to strings when used with the + operator in this manner. Java example | C# example. While JavaScript takes it to an extreme level, it stems from the language's early design principles favoring conversion over throwing errors. Both approaches aim for flexibility and accommodation, although as we now realize, it can sometimes lead to unexpected outcomes. :-)

Answer №2

Unlike Typescript, Eslint addresses the issue of implicit coercion with rules like this one and that one.

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