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    loadjs
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    4.2.0 • Public • Published

    LoadJS

    LoadJS is a tiny async loader for modern browsers (899 bytes).

    Dependency Status devDependency Status CDNJS

    Introduction

    LoadJS is a tiny async loading library for modern browsers (IE9+). It has a simple yet powerful dependency management system that lets you fetch JavaScript, CSS and image files in parallel and execute code after the dependencies have been met. The recommended way to use LoadJS is to include the minified source code of loadjs.js in your <html> (possibly in the <head> tag) and then use the loadjs global to manage JavaScript dependencies after pageload.

    LoadJS is based on the excellent $script library by Dustin Diaz. We kept the behavior of the library the same but we re-wrote the code from scratch to add support for success/error callbacks and to optimize the library for modern browsers. LoadJS is 899 bytes (minified + gzipped).

    Here's an example of what you can do with LoadJS:

    // define a dependency bundle and execute code when it loads
    loadjs(['/path/to/foo.js', '/path/to/bar.js'], 'foobar');
     
    loadjs.ready('foobar', function() {
      /* foo.js & bar.js loaded */
    });

    You can also use more advanced syntax for more options:

    // define a dependency bundle with advanced options
    loadjs(['/path/to/foo.js', '/path/to/bar.js'], 'foobar', {
      before: function(path, scriptEl) { /* execute code before fetch */ },
      async: true,  // load files synchronously or asynchronously (default: true)
      numRetries: 3  // see caveats about using numRetries with async:false (default: 0),
      returnPromise: false  // return Promise object (default: false)
    });
     
    loadjs.ready('foobar', {
      success: function() { /* foo.js & bar.js loaded */ },
      error: function(depsNotFound) { /* foobar bundle load failed */ },
    });

    The latest version of LoadJS can be found in the dist/ directory in this repository:

    You can also use it as a CJS or AMD module:

    $ npm install --save loadjs
    var loadjs = require('loadjs');
     
    loadjs(['/path/to/foo.js', '/path/to/bar.js'], 'foobar');
     
    loadjs.ready('foobar', function() {
      /* foo.js & bar.js loaded */
    });

    Browser Support

    • IE9+ (async: false support only works in IE10+)
    • Opera 12+
    • Safari 5+
    • Chrome
    • Firefox
    • iOS 6+
    • Android 4.4+

    LoadJS also detects script load failures from AdBlock Plus and Ghostery in:

    • Safari
    • Chrome

    Note: LoadJS treats empty CSS files as load failures in IE9-11 and uses rel="preload" to load CSS files in Edge (to get around lack of support for onerror events on <link rel="stylesheet"> tags)

    Documentation

    1. Load a single file

      loadjs('/path/to/foo.js', function() {
        /* foo.js loaded */
      });
    2. Fetch files in parallel and load them asynchronously

      loadjs(['/path/to/foo.js', '/path/to/bar.js'], function() {
        /* foo.js and bar.js loaded */
      });
    3. Fetch JavaScript, CSS and image files

      loadjs(['/path/to/foo.css', '/path/to/bar.png', 'path/to/thunk.js'], function() {
        /* foo.css, bar.png and thunk.js loaded */
      });
    4. Force treat file as CSS stylesheet

      loadjs(['css!/path/to/cssfile.custom'], function() {
        /* cssfile.custom loaded as stylesheet */
      });
    5. Force treat file as image

      loadjs(['img!/path/to/image.custom'], function() {
        /* image.custom loaded */
      });
    6. Add a bundle id

      loadjs(['/path/to/foo.js', '/path/to/bar.js'], 'foobar', function() {
        /* foo.js & bar.js loaded */
      });
    7. Use .ready() to define bundles and callbacks separately

      loadjs(['/path/to/foo.js', '/path/to/bar.js'], 'foobar');
       
      loadjs.ready('foobar', function() {
        /* foo.js & bar.js loaded */
      });
    8. Use multiple bundles in .ready() dependency lists

      loadjs('/path/to/foo.js', 'foo');
      loadjs(['/path/to/bar1.js', '/path/to/bar2.js'], 'bar');
       
      loadjs.ready(['foo', 'bar'], function() {
        /* foo.js & bar1.js & bar2.js loaded */
      });
    9. Chain .ready() together

      loadjs('/path/to/foo.js', 'foo');
      loadjs('/path/to/bar.js', 'bar');
       
      loadjs
        .ready('foo', function() {
          /* foo.js loaded */
        })
        .ready('bar', function() {
          /* bar.js loaded */
        });
    10. Use Promises to register callbacks

      loadjs(['/path/to/foo.js', '/path/to/bar.js'], {returnPromise: true})
        .then(function() { /* foo.js & bar.js loaded */ })
        .catch(function(pathsNotFound) { /* at least one didn't load */ });
    11. Check if bundle has already been defined

      if (!loadjs.isDefined('foobar')) {
        loadjs(['/path/to/foo.js', '/path/to/bar.js'], 'foobar', function() {
          /* foo.js & bar.js loaded */
        });
      }
    12. Fetch files in parallel and load them in series

      loadjs(['/path/to/foo.js', '/path/to/bar.js'], {
        success: function() { /* foo.js and bar.js loaded in series */ },
        async: false
      });
    13. Add an error callback

      loadjs(['/path/to/foo.js', '/path/to/bar.js'], 'foobar', {
        success: function() { /* foo.js & bar.js loaded */ },
        error: function(pathsNotFound) { /* at least one path didn't load */ }
      });
    14. Retry files before calling the error callback

      loadjs(['/path/to/foo.js', '/path/to/bar.js'], 'foobar', {
        success: function() { /* foo.js & bar.js loaded */ },
        error: function(pathsNotFound) { /* at least one path didn't load */ },
        numRetries: 3
      });
       
      // NOTE: Using `numRetries` with `async: false` can cause files to load out-of-sync on retries
    15. Execute a callback before script tags are embedded

      loadjs(['/path/to/foo.js', '/path/to/bar.js'], {
        success: function() {},
        error: function(pathsNotFound) {},
        before: function(path, scriptEl) {
          /* called for each script node before being embedded */
          if (path === '/path/to/foo.js') scriptEl.crossOrigin = true;
        }
      });
    16. Bypass LoadJS default DOM insertion mechanism (DOM <head>)

      loadjs(['/path/to/foo.js'], {
        success: function() {},
        error: function(pathsNotFound) {},
        before: function(path, scriptEl) {
          document.body.appendChild(scriptEl);
        
          /* return `false` to bypass default DOM insertion mechanism */
          return false;
        }
      });
    17. Use bundle ids in error callback

      loadjs('/path/to/foo.js', 'foo');
      loadjs('/path/to/bar.js', 'bar');
      loadjs(['/path/to/thunkor.js', '/path/to/thunky.js'], 'thunk');
       
      // wait for multiple depdendencies
      loadjs.ready(['foo', 'bar', 'thunk'], {
        success: function() {
          // foo.js & bar.js & thunkor.js & thunky.js loaded
        },
        error: function(depsNotFound) {
          if (depsNotFound.indexOf('foo') > -1) {};  // foo failed
          if (depsNotFound.indexOf('bar') > -1) {};  // bar failed
          if (depsNotFound.indexOf('thunk') > -1) {};  // thunk failed
        }
      });
    18. Use .done() for more control

      loadjs.ready(['dependency1', 'dependency2'], function() {
        /* run code after dependencies have been met */
      });
       
      function fn1() {
        loadjs.done('dependency1');
      }
       
      function fn2() {
        loadjs.done('dependency2');
      }
    19. Reset dependency trackers

      loadjs.reset();
    20. Implement a require-like dependency manager

      var bundles = {
        'bundleA': ['/file1.js', '/file2.js'],
        'bundleB': ['/file3.js', '/file4.js']
      };
       
      function require(bundleIds, callbackFn) {
        bundleIds.forEach(function(bundleId) {
          if (!loadjs.isDefined(bundleId)) loadjs(bundles[bundleId], bundleId);
        });
        loadjs.ready(bundleIds, callbackFn);
      }
       
      require(['bundleA'], function() { /* bundleA loaded */ });
      require(['bundleB'], function() { /* bundleB loaded */ });
      require(['bundleA', 'bundleB'], function() { /* bundleA and bundleB loaded */ });

    Directory structure

    loadjs/
    ├── dist
    │   ├── loadjs.js
    │   ├── loadjs.min.js
    │   └── loadjs.umd.js
    ├── examples
    ├── gulpfile.js
    ├── LICENSE.txt
    ├── package.json
    ├── README.md
    ├── src
    │   └── loadjs.js
    ├── test
    └── umd-templates
    

    Development Quickstart

    1. Install dependencies

    2. Clone repository

      $ git clone git@github.com:muicss/loadjs.git
      cd loadjs
    3. Install node dependencies using npm

      $ npm install
    4. Build examples

      $ npm run build-examples

      To view the examples you can use any static file server. To use the nodejs http-server module:

      $ npm install http-server
      $ npm run http-server -- -p 3000

      Then visit http://localhost:3000/examples

    5. Build distribution files

      $ npm run build-dist

      The files will be located in the dist directory.

    6. Run tests

      To run the browser tests first build the loadjs library:

      $ npm run build-tests

      Then visit http://localhost:3000/test

    7. Build all files

      $ npm run build-all

    Install

    npm i loadjs

    DownloadsWeekly Downloads

    219,721

    Version

    4.2.0

    License

    MIT

    Unpacked Size

    958 kB

    Total Files

    56

    Last publish

    Collaborators

    • muicss