esm-import-transformer

esm-import-transformer

Can transform any ESM source code import URLs using an import maps object. This package works in ESM or CJS.

// Input source code:
import {html, css, LitElement} from "lit";

// Transform with an import map:
import {html, css, LitElement} from "https://cdn.jsdelivr.net/gh/lit/dist@2/core/lit-core.min.js";

// Or transform to a dynamic import:
const {html, css, LitElement} = await import("lit");

// Or transform to CommonJS require:
const {html, css, LitElement} = require("lit");

Usage

// ESM
import { ImportTransformer } from "esm-import-transformer";

// or CJS
const { ImportTransformer } = await import("esm-import-transformer");

Transform with an import map

Pass in a source code string and an import maps object.

let sourceCode = `import {html, css, LitElement} from "lit";`;
let it = new ImportTransformer(sourceCode);

let importMap = {
  imports: {
    lit: "https://cdn.jsdelivr.net/gh/lit/dist@2/core/lit-core.min.js"
  }
};
let outputCode = it.transformWithImportMap(importMap);
// returns: `import {html, css, LitElement} from "https://cdn.jsdelivr.net/gh/lit/dist@2/core/lit-core.min.js";`

Transform to dynamic import()

let sourceCode = `import {html, css, LitElement} from "lit";`;
let it = new ImportTransformer(sourceCode);

let outputCode = it.transformToDynamicImport();
// returns: `const {html, css, LitElement} = await import("lit");`

Transform to require()

Added in v3.0.1: This method does not require that the downstream package is CommonJS, but remember that running the resulting code will fail if you try to require an ESM package (in some JavaScript environments, e.g. Node < 20).

let sourceCode = `import {html, css, LitElement} from "lit";`;
let it = new ImportTransformer(sourceCode);

let outputCode = it.transformToRequire();
// returns: `const {html, css, LitElement} = require("lit");`

Has imports?

Added in v3.0.2 Returns true if the code has any top level import.

let sourceCode = `import {html, css, LitElement} from "lit";`;
let it = new ImportTransformer(sourceCode);
it.hasImports(); // true

let sourceCode = `const {html, css, LitElement} = require("lit");`;
let it = new ImportTransformer(sourceCode);
it.hasImports(); // false

Installation

Available on npm

npm install esm-import-transformer