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From: Thomas 'PointedEars' Lahn <PointedEars@web.de>
Newsgroups: comp.lang.javascript
Subject: Re: Why is it so convoluted to import a .js file in javascript?
Date: Thu, 27 Mar 2014 22:29:03 +0100
Organization: PointedEars Software (PES)
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References: <d1050ce2-5b06-4bb8-9d69-18cc325b30c0@googlegroups.com> <include-20140327003813@ram.dialup.fu-berlin.de>
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Xref: csiph.com comp.lang.javascript:23713

Stefan Ram wrote:

> jonas.thornvall@gmail.com writes:
>> // load math.js and create an instance
>> var mathjs = require('math,js'),
> 
>   s/,/./
> 
>   The method »require« is a method of the modules API of
>   Node.js,

ACK.

>   it is not a part of standard JavaScript AFAIK.

There is no “standard JavaScript”; the various implementations/languages 
that call themselves „JavaScript“ (most notably: JavaScript™, JScript, V8, 
Opera ECMAScript, and KJS) are *implementations of* a(n Ecma) standard, the 
ECMAScript Language Specification (ECMA-262).  Conforming implementations of 
ECMAScript *may extend* the Specification’s algorithms and syntax:

<http://PointedEars.de/es-matrix>

This function is not specified in ECMAScript (yet?), and AFAIK it is not 
available in any „JavaScript“.  In Node.js, it is a feature provided by the 
host environment that runs V8 JavaScript:

<http://nodejs.org/api/modules.html>
 
>>Why can't a simple
>>import('../test/test.js'); or append('../test/test.js');
>>do?
> 
>   When JavaScript is running in a web browser, scripts can be
>   loaded in HTML using
> 
> <script type="text/javascript" src="../test/test.js"></script>

“script” elements can also be inserted dynamically, causing the script code 
to be loaded, which is closest to Node.js's approach.  I do not think this 
is limited to HTML.

However, for this to work reliably, the host environment must support either 
a way to determine when the script resource has been loaded (and parsed) – 
this is available in a so far conforming implementation of W3C DOM Level 3 
Events (WD) [1] – or synchronous XHR (which allows the normal program flow 
to continue only after the resource has been loaded; the usual caveats 
apply).

An example for the former is:

  function require (source, callback)
  {
    var script = document.createElement("script");
    script.addEventListener("load", callback);
    script.src = source;

    /* HTML5/WHATWG HTML only */
    document.head.appendChild(script);
  }

  require("http://script.example/foo.js", function () {
    console.log("Script loaded");
  });

(There are libraries that implement and improve this or a similar approach; 
so far none can be recommended, none can be recommended against.  Use it and 
them with caution.)

A proof of concept for the latter is provided by jsx.importFrom() and 
jsx.importOnce() in JSX:object.js [2]
 
>   . JavaScript does not have a means to import a file itself.
>   Maybe because it does not want to include features specific
>   to only some environments, such as filesystem access.

ACK.

________
[1] <http://www.w3.org/TR/DOM-Level-3-Events/#event-type-load>
[2] <http://PointedEars.de/wsvn/JSX/trunk/object.js>
    (Note that jsx.require() does _not_ implement the asynchronous approach
    yet.)
-- 
PointedEars

Twitter: @PointedEars2
Please do not Cc: me. / Bitte keine Kopien per E-Mail.