Enable browser mode
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. It also sets the global object to window
, and aims to simulate the browser as realistically as possible.
/* [CommonJS] */
require('enable-browser-mode');
- or -
/* [ES6] */
import 'enable-browser-mode'
No variable assignment required, just call it! You can then require browser JS with:
include('./jquery.min.js');
Which will evaluate that script in the global context. (Make sure the scripts supplied to window.include()
are trusted.)
Example
Won't work:
console.log(document.createElement('a'));
> ReferenceError: document is not defined
Works like a charm:
require('enable-browser-mode');
console.log(document.createElement('a'));
> HTMLAnchorElement {Symbol(impl): HTMLAnchorElementImpl}
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, web-widgets
builds out the widget tree on the virtual DOM and then exports it as flat HTML using the Node.outerHTML
property, and in the browser, the DOM is manipulated directly on-the-fly (i.e. with Node.appendChild
). With enable-browser-window
, all that is needed to reuse the original browser library is creating an separate JS file for Node, importing this package, and then importing your browser code:
require('enable-browser-mode');
require('browser.js');
myBrowserObject.doBrowserStuff();
// code like you're in the browser =)
Implementation
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;
Digressions
It should really take zero extra 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!