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Minimalist AMD-compliant Javascript and CSS loader

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lockandload AMD-loader

Lockandload is a minimalist AMD-loader-compatible boilerplate to kickstart your website. It includes special support for single-page-apps.

Gzipped, the essential script content amounts to roughly 849 bytes of code. Without compression it blows up to about 1449 bytes. Further minifying this code does not result in any significant gains (773 vs 849 bytes), it would just hinder readability.

Why

After reviewing the javascript-loader landscape, looking for a loader that satisfies the following criteria:

  • Small enough to be inlined (to avoid paying an extra request-tax to get the loader onboard).
  • Inlined config file (get rid of a request).
  • Config file in pure javascript (no parsing overhead).
  • Let the browser do the actual loading (browsers are smart these days) of files.
  • Connect all asynchronously loaded modules together.
  • Support for single page apps that include legacy code that uses sprinkled $(function(){...}) constructs, yet I insist on loading jQuery late and asynchronously to speed things up.

I came to the conclusion that (apparently?) none of the existing loaders fit the bill. So I wrote lockandload back in 2014 and used it in various internal projects, but decided to open-source it now in case others find it useful. As always, when open-sourcing something, actually writing documentation takes most of the time. The documentation can always be improved. Suggestions are welcome!

Features

  • Zero dependencies.
  • Less filling: 849 bytes of gzipped script content.
  • Handminified to retain readable and maintainable code.
  • It's so small, it can and should be inlined on your HTML page (which is also one of the reasons to handminify it only).
  • Because it is inlined, it is faster than all other loaders.
  • Fully asynchronous script loader: AMD-loader compatible.
  • Supports anonymous define() calls.
  • Supports local require() calls (with one and two arguments, RequireJS-style).
  • Supports require.undef() for hot-reloading scripts.
  • Supports require.load() to load scripts on demand.
  • Supports implicit and explicit ['require', 'exports', 'module'] dependencies.
  • Explicit circular dependencies will hang silently in an unresolved state (or put differently: do not do that), use 'exports' or 'require' to resolve those instead.
  • No extra diagnostic code to minimise code weight and optimise loading speed.
  • Does not support require.toUrl() nor simplified CommonJS wrapping.
  • Fully event driven, no polling timers.
  • Standard supported dependencies: require, exports, module and domready.
  • Both high and low priority asynchronous loading of Javascript and CSS files.
  • Leverages native browser speed for high priority loading (by getting out of the way; let <script>, HTTP2 and friends do the heavy lifting).
  • Legacy support for $(...) jQuery riddled synchronous code.
  • Legacy support for loading synchronous Javascript.
  • Single-page-app support using $$(...) page refresh callbacks.
  • Supports browsers implementing ES2018 and up.
  • No config file, means: no syntax to learn, no config file parser code.
  • No module system: all needed functionality is included already because it was/is so small, that writing a module system would take more code than the source of all the added functionality.
  • Integrated hooks for Google Tag Manager (GTM) support.

Requirements

It runs inside any webbrowser environment (supporting ES2018 and up).

Usage

Using npm

Running npm install lockandload in the webroot of your site, should create the following file and directory structure:

  • node_modules
    • lockandload
      • lockandload_master.inc: Placed right after the charset definition on the page.
      • lockandload_headready.inc: The start of the headready-script that lives at the end of the <head>.
      • lockandload_trailer.inc: The end of the headready-script that lives at the end of the <head>.
      • lockandload_master_debug.inc: Alternate debugging version of lockandload_master.inc.
      • index.php: PHP boilerplate.
      • index_inlined.html: High performance HTML only boilerplate.
      • lockandload_master.js: For lazy <script> loading.
      • lockandload_master_debug.js: Alternate debugging version of lockandload_master.js.
      • lockandload_headready.js: Boilerplate for lazy <script> loading.
      • index_extern.html: Lazy HTML only boilerplate.
      • main.js: Example SPA (Single Page Application).

Using PHP

Copy the boilerplate node_modules/lockandload/index.php file to your webroot; then customise the copied file to taste.

Using other serverside scripting languages

Look at the PHP boilerplate node_modules/lockandload/index.php, and translate this to your own scripting language.

Without serverside scripting (lazy)

Copy the node_modules/lockandload/index_extern.html boilerplate file to your webroot; then customise the copied file to taste. Copy the node_modules/lockandload/lockandload_headready.js file to your javascript directory and customise it taste. Do not forget to change the path of the script directive in index_extern.html to point to the new location of the headready script.

Without serverside scripting (high performance)

Copy the node_modules/lockandload/index_inlined.html boilerplate file to your webroot; then customise the copied file to taste. The index_inlined.html contains two <script> sections. The first section should not be preceded by any other <script> tags and should be left verbatim.

The second section should be placed at or close to the end of the <head>, and should not precede any direct <link type="stylesheet"> tags. Inside this second section there is a clearly marked section that is your configuration area.

The basic structure of a page should be:

  • html
    • head
      • Charset declaration.
      • Inline lockandload master script.
      • High priority async external scripts.
      • Viewport declaration.
      • High priority CSS scripts.
      • <title>.
      • All other tags that should go in the <head>.
      • Inline lockandload headready-script.
        • CSS scripts fullfilling a custom applied-style dependency.
        • Low priority CSS scripts.
        • Medium priority async Javascript scripts.
        • Low priority async Javascript scripts.
        • Low priority synchronous Javascript scripts.
    • body
      • All other inline scripts (if you must).

The index_inlined.html file is a production-stripped version of annotated.html. Look at annotated.html to understand the code and read additional inline documentation. These index.*, lockandload_*.inc and lockandload_*.js files are not present in the git source repository, they can only be found in the npm repository (or after running npm run prepublish).

API

Module ids

Module ids are short strings that uniquely identify a module. In lockandload these ids typically do not contain parts of a path. If a module id is derived from the javascript filename that is being loaded, it will only refer to the final path component without .js or version extension (i.e. anything after the last / and before the first .).

Globally

  • define(id?, dependencies?, factory)
    The standard AMD global entrypoint.

    • id declares the module id we are defining. If omitted, we derive a module id from the name of the javascript file we are loading.
    • dependencies is an array of strings of module ids this module depends on. If the parameter is missing, a default dependency list of ["require", "exports", "module"] is supplied.
    • factory is the callback function that gets called as soon as all dependencies have been loaded. The factory function gets references to all the exported symbols from its dependencies, and should subsequently return its own symbols it wants to export to other modules. The factory can be a function or a static object.

  • require(dependencies, callback)
    Allows you to load dependencies (an array of strings of module ids) asynchronously, the callback is called as soon as all dependencies have loaded. Parameters to the callback are references to the dependencies just as in the factory function in define.

Locally

In the secondary lockandload headready-script; all url arguments are used verbatim in <link href="url"> or <script src="url"> tags:

  • css(url, id?)
    Loads low priority ordered css files asynchronously; after the stylesheet has been applied, it fulfills the optional id dependency.
  • js(url, "async"?, noCORS?)
    Loads Javascript file. If the second optional argument "async" is provided, the load will be asynchronous. If the third optional argument is true, the script will be loaded without crossOrigin parameter (typically needed to load GTM).
  • jsa(alias, path)
    Define aliases for javascript file paths to be referenced through require.load(alias) to load the file on demand.

Standard require module

If you use "require" in your dependencylist, you get a reference to the internal require-module (which behaves identical to the global require()). It supports the following functionality:

  • require(id)
    Returns a reference to the exports of module id. Beware: this will not trigger loading that module, if the module is not loaded because it was already in your dependencylist, or if the module is not being requested by other modules, this will return zero. As such, it can be used to find out if a certain module is being loaded at all.
  • require.undef(id)
    Clears the cached module id exported symbols list. This allows the module to be hot-reloaded by a subsequent require.load(). Beware that existing references to the old module are not overwritten. Any modules using require(id) before the require.load() will return zero, any modules using require(id) after the require.load() will return a reference to the exports of the reloaded module.
  • require.load(file)
    Asynchronously loads the referenced javascript file. To centralise file-location management, it is advisable to use jsa() calls in the headready section to declare aliases for javascript files which can be used instead of actual file paths in the require.load() calls.

Dealing with jQuery

In order to support legacy code that uses inline $(function(){...}) scattered throughout pages, this loader allows you to use that construct even before the jQuery library has been loaded, and thus enables you to load jQuery in an asynchronous and non-blocking fashion.

N.B. Use the jQuery dependency instead of plain jquery to avoid a race for an undefined window.$ object.

SPA (Single Page App) support

To ease SPA development, the loader defines a $$(function(jquery_document){...}) function which registers functions for execution on every SPA-controlled page refresh. The registered functions receive a convenience argument $(document) when executed.

To run the registered functions, one needs to make a call to the entrypoint of the AMD-dependency on domready without parameters or with exactly one parameter; if not provided, this single parameter will default to $(document) (the jquery object/scope referring to the whole document). Convention states that if provided the argument should normally be the jquery object referring to the element tree that contains the changes. Ultimately you decide what your $$(function(argument){...}) scheduled scripts will use the argument for. All domready() calls before domready(1) has been run will be silently ignored.

E.g. in your application, you could use code like this:

!function(){
  // Preamble
  define("main", ["domready"], function (domready) {
    // Your main application
    function refreshpage() {
      // The function that gets called on virtual page refreshes
      var newdiv = $("#contentdiv");
      newdiv.html("your glorious new page content");
      domready(newdiv);   // This will call all registered $$(...) functions
                          // with the newdiv as argument to potentially
                          // limit the scope of the changes
    }
  });
}();

References

Other AMD-loaders:

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Minimalist AMD-compliant Javascript and CSS loader

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