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# esm-import-transformer
Can transform any ESM source code `import` URLs using an import maps object. This package works in ESM or CJS.
```js
// 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
```js
// 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](https://github.com/WICG/import-maps) object.
```js
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()`
```js
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).
```js
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`.
```js
let sourceCode = `import {html, css, LitElement} from "lit";`;
let it = new ImportTransformer(sourceCode);
it.hasImports(); // true
```
```js
let sourceCode = `const {html, css, LitElement} = require("lit");`;
let it = new ImportTransformer(sourceCode);
it.hasImports(); // false
```
## Installation
Available on [npm](https://www.npmjs.com/package/esm-import-transformer)
```
npm install esm-import-transformer
```
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