What is the best method for importing CommonJS into TypeScript while maintaining forward compatibility?

Question

What is the best method for importing CommonJS into TypeScript while maintaining forward compatibility?

In terms of future compatibility with both TypeScript and the ES module spec, which method is the most reliable for importing a CommonJS module?

import * as foo from "foo
```
import foo = require("foo")
```
```
const foo = require("foo")
```

If the "foo" library transitions to using ES modules in the future, which of the above approaches is least likely to cause issues or behave unexpectedly?

Update: Method (1) appears to be the most promising since it closely aligns with true ES Module syntax. However, there are concerns about maintaining the intended semantics of the original CommonJS module being imported. It is important to ensure that any expected side effects still occur when using the import * as syntax.

Another update: Our target is ultimately ES modules. A separate tool will handle the transformation from ES Modules to the desired format.

typescript commonjs es6-modules

Answer 1

Answer №1

const bar = require("bar")

This particular method is not recommended, as bar will be inferred as type any. It's best to avoid using this approach altogether.

import bar = require("bar")

Using this TypeScript-specific import syntax is also discouraged. Although it provides type safety during compile time by being compiled to var bar = require("bar") at runtime, it should still be avoided whenever possible. This method is primarily used for importing modules that utilize export assignment.

import * as bar from "bar"

Instead, favor the official ES2015 syntax when importing modules, as shown above. This syntax should be preferred in most cases, except when dealing with export assignments.

When compiling to commonjs, the above syntax will be transpiled to const bar = require("./bar"); at runtime, ensuring consistent behavior.

It's important to note that TypeScript will not emit imports that are unused or used solely for their types (refer to the explanation here). If you need to import a module for side effects, you can use the following syntax:

import "bar"

Answer 2

const bar = require("bar")

This particular method is not recommended, as bar will be inferred as type any. It's best to avoid using this approach altogether.

import bar = require("bar")

Using this TypeScript-specific import syntax is also discouraged. Although it provides type safety during compile time by being compiled to var bar = require("bar") at runtime, it should still be avoided whenever possible. This method is primarily used for importing modules that utilize export assignment.

import * as bar from "bar"

Instead, favor the official ES2015 syntax when importing modules, as shown above. This syntax should be preferred in most cases, except when dealing with export assignments.

When compiling to commonjs, the above syntax will be transpiled to const bar = require("./bar"); at runtime, ensuring consistent behavior.

It's important to note that TypeScript will not emit imports that are unused or used solely for their types (refer to the explanation here). If you need to import a module for side effects, you can use the following syntax:

import "bar"

What is the best method for importing CommonJS into TypeScript while maintaining forward compatibility?

Answer №1

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