same file name in typescript files and javascript files

Question

Let's say in the src folder, we have two files, one is typescript file someFeatures.ts, the other is js file someFeatures.js,so their main file name is the same, and contain the same content,just the extension name is different, so in the main index.ts file, I import the dependency as:

import { sizeFormatter, costFormatter } from "./someFeatures";

so how does the compile know which one I'm referring to? it could be someFeatures.ts or someFeatures.js?

Answer 1

allowJS: false

If the allowJs option in tsconfig.json is set to false then Typescript compiler will ignore someFeatures.js like any .js file when it resolves imports. It will take only .ts .tsx .d.ts into account as explained here under How TypeScript resolves modules heading.

allowJS: true

If the allowJs option in tsconfig.json is set to true then Typescript compiler will specifically ignore someFeatures.js as a "possible output" due to presence of someFeatures.tsas explained there, search for "possible outputs".