What is this for?

Properly converting NodeJS require statements to EcmaScript import statments (using the Tree Sitter parser NOT REGEX, like all the other tools out there). Works for JavaScript.

How do I use it?

There’s a CLI, a backend interface, and a client-side interface.

CLI

Install

# isntall deno
curl -fsSL https://deno.land/install.sh | sh
# install to-esm
deno install -Afg https://deno.land/x/to_esm/main/to-esm.js

Usage:

# non-destructive, creates file1.esm.js, look for "CHECKME" comments
to-esm ./file1.js

# destructive
to-esm --inplace ./file1.js
to-esm -i ./file1.js

# recursive
to-esm --recursive .
to-esm -r .

# choose the rename extension (file1.fixed.js)
to-esm --add-ext .fixed -- ./file1.js

NOTE: there will never be a perfect conversion. Check the output for CHECKME and FIXME comments for the cases where there were problems.

Backend API

import { toEsm } from "https://deno.land/x/to_esm/main/impure_api.js"

// only does one file at a time
const newFileContent = await toEsm({
    path: "./file1.js", 
    customConverter: (importPathString, path) => {
        // convert all npm stuff to esm.sh
        if (importPathString.startsWith("npm:")) {
            return JSON.stringify("https://esm.sh/${importPathString.slice(4)}")
        }
        if (importPathString === "b") {
            return JSON.stringify("https://deno.land/x/a@1.2.3/mod.js")+" // CHECKME "
        } 
    },
    // if you want to hack an edge case for your own project
    handleUnhandlable: (requireArgs, statementText, statement) => {
        // if the require args are "b" or 'b'
        if (requireArgs.match(/("|')b(\1)/)) {
            return `import { a } from "https://deno.land/x/a@1.2.3/mod.js" // CHECKME`
        }
    }
})

Frontend API

Note: the frontend API can’t do as much as the backend API because it can’t scan the file system to make intelligent guesses.

import { convertImports } from "https://deno.land/x/to_esm/main/pure_api.js"

const newFileContent = await convertImports({
    fileContent: `require("something")`,
    path,
    defaultExtension=".js",
})