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enable-window-document

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enable-window-document

Enables "window" and "document" globals so browser code does not throw errors in Node. Built with JSDOM.

  • 1.4.0
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  • npm
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Enable window and document

The goal of this package is to work as a quick-and-dirty one-liner that will allow Node to require and otherwise execute traditional browser code without throwing errors. Simply set the window and document globals with:

require('enable-window-document');

No variable assignment required, just call it!

Use cases

The specific need for this functionality came from the web-widgets package, which generates widget trees using DOM operations like document.createElement(). The Node runtime cannot build out this widget tree by default, as it does not have access to the window and document variables, so it throws a ReferenceError.

By importing this package (which depends on JSDOM), we can expose the window and document globals to the whole project, meaning we can write all of our browser-optimized (and DOM-heavy) code in a file like browser.js, but still use that same code for server-side rendering in Node with require('browser.js').

In Node, the widget tree is built out in the virtual DOM and then exported as flat HTML with outerHTML. In the browser, the DOM is manipulated directly on-the-fly (i.e. with Node.appendChild).

Additionally, we can Closure Compile our browser code before depending on it in Node, meaning builds are as small and performant as possible. No webpack, no extra polyfills.

Behind the scenes

This package simply creates a blank JSDOM with four lines of code, and stores the global window and document variables, which point to the empty DOM:

let JSDOM = require('jsdom'),
    DOM = new JSDOM.JSDOM(`<html><body></body></html>`);

global.window = DOM.window,
global.document = window.document;

Example

Won't work:

console.log(document.createElement('a'));

>   ReferenceError: document is not defined

Works like a charm:

require('enable-window-document');
console.log(document.createElement('a'));

>   HTMLAnchorElement {Symbol(impl): HTMLAnchorElementImpl}

Digressions

It should really take zero lines to run browser-compatible JS in Node, but one line will do for now. The important part is that instead of writing everything for Node and then using browserify and other tools to polyfill it for the browser, we can write strict code for the browser and force Node to interpret Javascript in the same way the browser does.

Why the Node runtime does not expose window and document OOTB is a valid question, as whatever rationale exists behind that decision cannot be more concrete than the principle that code which can execute in a browser should be able to execute in the Node runtime. Javascript output from one environment should === the same Javascript run in another. It's supposed to be a lingua franca!

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Package last updated on 10 Jun 2020

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