How do I include a JavaScript file in another JavaScript file?



Answers

If anyone is looking for something more advanced, try out RequireJS. You'll get added benefits such as dependency management, better concurrency, and avoid duplication (that is, retrieving a script more than once).

You can write your JavaScript files in "modules" and then reference them as dependencies in other scripts. Or you can use RequireJS as a simple "go get this script" solution.

Example:

Define dependencies as modules:

some-dependency.js

define(['lib/dependency1', 'lib/dependency2'], function (d1, d2) {

     //Your actual script goes here.   
     //The dependent scripts will be fetched if necessary.

     return libraryObject;  //For example, jQuery object
});

implementation.js is your "main" JavaScript file that depends on some-dependency.js

require(['some-dependency'], function(dependency) {

    //Your script goes here
    //some-dependency.js is fetched.   
    //Then your script is executed
});

Excerpt from the GitHub README:

RequireJS loads plain JavaScript files as well as more defined modules. It is optimized for in-browser use, including in a Web Worker, but it can be used in other JavaScript environments, like Rhino and Node. It implements the Asynchronous Module API.

RequireJS uses plain script tags to load modules/files, so it should allow for easy debugging. It can be used simply to load existing JavaScript files, so you can add it to your existing project without having to re-write your JavaScript files.

...

Question

Is there something in JavaScript similar to @import in CSS that allows you to include a JavaScript file inside another JavaScript file?




Another way, that in my opinion is much cleaner, is to make a synchronous Ajax request instead of using a <script> tag. Which is also how Node.js handles includes.

Here's an example using jQuery:

function require(script) {
    $.ajax({
        url: script,
        dataType: "script",
        async: false,           // <-- This is the key
        success: function () {
            // all good...
        },
        error: function () {
            throw new Error("Could not load script " + script);
        }
    });
}

You can then use it in your code as you'd usually use an include:

require("/scripts/subscript.js");

And be able to call a function from the required script in the next line:

subscript.doSomethingCool(); 



Better use the jQuery way. To delay the ready event, first call $.holdReady(true). Example (source):

$.holdReady(true);
$.getScript("myplugin.js", function() {
    $.holdReady(false);
});



It is possible to dynamically generate a JavaScript tag and append it to HTML document from inside other JavaScript code. This will load targeted JavaScript file.

function includeJs(jsFilePath) {
    var js = document.createElement("script");

    js.type = "text/javascript";
    js.src = jsFilePath;

    document.body.appendChild(js);
}

includeJs("/path/to/some/file.js");



There are a lot of potential answers for this question. My answer is obviously based on a number of them. This is what I ended up with after reading through all the answers.

The problem with $.getScript and really any other solution that requires a callback when loading is complete is that if you have multiple files that use it and depend on each other you no longer have a way to know when all scripts have been loaded (once they are nested in multiple files).

Example:

file3.js

var f3obj = "file3";

// Define other stuff

file2.js:

var f2obj = "file2";
$.getScript("file3.js", function(){

    alert(f3obj);

    // Use anything defined in file3.
});

file1.js:

$.getScript("file2.js", function(){
    alert(f3obj); //This will probably fail because file3 is only guaranteed to have loaded inside the callback in file2.
    alert(f2obj);

    // Use anything defined in the loaded script...
});

You are right when you say that you could specify Ajax to run synchronously or use XMLHttpRequest, but the current trend appears to be to deprecate synchronous requests, so you may not get full browser support now or in the future.

You could try to use $.when to check an array of deferred objects, but now you are doing this in every file and file2 will be considered loaded as soon as the $.when is executed not when the callback is executed, so file1 still continues execution before file3 is loaded. This really still has the same problem.

I decided to go backwards instead of forwards. Thank you document.writeln. I know it's taboo, but as long as it is used correctly this works well. You end up with code that can be debugged easily, shows in the DOM correctly and can ensure the order the dependencies are loaded correctly.

You can of course use $ ("body").append(), but then you can no longer debug correctly any more.

NOTE: You must use this only while the page is loading, otherwise you get a blank screen. In other words, always place this before / outside of document.ready. I have not tested using this after the page is loaded in a click event or anything like that, but I am pretty sure it'll fail.

I liked the idea of extending jQuery, but obviously you don't need to.

Before calling document.writeln, it checks to make sure the script has not already been loading by evaluating all the script elements.

I assume that a script is not fully executed until its document.ready event has been executed. (I know using document.ready is not required, but many people use it, and handling this is a safeguard.)

When the additional files are loaded the document.ready callbacks will get executed in the wrong order. To address this when a script is actually loaded, the script that imported it is re-imported itself and execution halted. This causes the originating file to now have its document.ready callback executed after any from any scripts that it imports.

Instead of this approach you could attempt to modify the jQuery readyList, but this seemed like a worse solution.

Solution:

$.extend(true,
{
    import_js : function(scriptpath, reAddLast)
    {
        if (typeof reAddLast === "undefined" || reAddLast === null)
        {
            reAddLast = true; // Default this value to true. It is not used by the end user, only to facilitate recursion correctly.
        }

        var found = false;
        if (reAddLast == true) // If we are re-adding the originating script we do not care if it has already been added.
        {
            found = $('script').filter(function () {
                return ($(this).attr('src') == scriptpath);
            }).length != 0; // jQuery to check if the script already exists. (replace it with straight JavaScript if you don't like jQuery.
        }

        if (found == false) {

            var callingScriptPath = $('script').last().attr("src"); // Get the script that is currently loading. Again this creates a limitation where this should not be used in a button, and only before document.ready.

            document.writeln("<script type='text/javascript' src='" + scriptpath + "'></script>"); // Add the script to the document using writeln

            if (reAddLast)
            {
                $.import_js(callingScriptPath, false); // Call itself with the originating script to fix the order.
                throw 'Readding script to correct order: ' + scriptpath + ' < ' + callingScriptPath; // This halts execution of the originating script since it is getting reloaded. If you put a try / catch around the call to $.import_js you results will vary.
            }
            return true;
        }
        return false;
    }
});

Usage:

File3:

var f3obj = "file3";

// Define other stuff
$(function(){
    f3obj = "file3docready";
});

File2:

$.import_js('js/file3.js');
var f2obj = "file2";
$(function(){
    f2obj = "file2docready";
});

File1:

$.import_js('js/file2.js');

// Use objects from file2 or file3
alert(f3obj); // "file3"
alert(f2obj); // "file2"

$(function(){
    // Use objects from file2 or file3 some more.
    alert(f3obj); //"file3docready"
    alert(f2obj); //"file2docready"
});



I wrote a simple module that automates the job of importing/including module scripts in JavaScript. For detailed explanation of the code, refer to the blog post JavaScript require / import / include modules.

// ----- USAGE -----

require('ivar.util.string');
require('ivar.net.*');
require('ivar/util/array.js');
require('http://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js');

ready(function(){
    //Do something when required scripts are loaded
});

    //--------------------

var _rmod = _rmod || {}; //Require module namespace
_rmod.LOADED = false;
_rmod.on_ready_fn_stack = [];
_rmod.libpath = '';
_rmod.imported = {};
_rmod.loading = {
    scripts: {},
    length: 0
};

_rmod.findScriptPath = function(script_name) {
    var script_elems = document.getElementsByTagName('script');
    for (var i = 0; i < script_elems.length; i++) {
        if (script_elems[i].src.endsWith(script_name)) {
            var href = window.location.href;
            href = href.substring(0, href.lastIndexOf('/'));
            var url = script_elems[i].src.substring(0, script_elems[i].length - script_name.length);
            return url.substring(href.length+1, url.length);
        }
    }
    return '';
};

_rmod.libpath = _rmod.findScriptPath('script.js'); //Path of your main script used to mark
                                                   //the root directory of your library, any library.


_rmod.injectScript = function(script_name, uri, callback, prepare) {

    if(!prepare)
        prepare(script_name, uri);

    var script_elem = document.createElement('script');
    script_elem.type = 'text/javascript';
    script_elem.title = script_name;
    script_elem.src = uri;
    script_elem.async = true;
    script_elem.defer = false;

    if(!callback)
        script_elem.onload = function() {
            callback(script_name, uri);
        };
    document.getElementsByTagName('head')[0].appendChild(script_elem);
};

_rmod.requirePrepare = function(script_name, uri) {
    _rmod.loading.scripts[script_name] = uri;
    _rmod.loading.length++;
};

_rmod.requireCallback = function(script_name, uri) {
    _rmod.loading.length--;
    delete _rmod.loading.scripts[script_name];
    _rmod.imported[script_name] = uri;

    if(_rmod.loading.length == 0)
        _rmod.onReady();
};

_rmod.onReady = function() {
    if (!_rmod.LOADED) {
        for (var i = 0; i < _rmod.on_ready_fn_stack.length; i++){
            _rmod.on_ready_fn_stack[i]();
        });
        _rmod.LOADED = true;
    }
};

_.rmod = namespaceToUri = function(script_name, url) {
    var np = script_name.split('.');
    if (np.getLast() === '*') {
        np.pop();
        np.push('_all');
    }

    if(!url)
        url = '';

    script_name = np.join('.');
    return  url + np.join('/')+'.js';
};

//You can rename based on your liking. I chose require, but it
//can be called include or anything else that is easy for you
//to remember or write, except "import", because it is reserved
//for future use.
var require = function(script_name) {
    var uri = '';
    if (script_name.indexOf('/') > -1) {
        uri = script_name;
        var lastSlash = uri.lastIndexOf('/');
        script_name = uri.substring(lastSlash+1, uri.length);
    } 
    else {
        uri = _rmod.namespaceToUri(script_name, ivar._private.libpath);
    }

    if (!_rmod.loading.scripts.hasOwnProperty(script_name)
     && !_rmod.imported.hasOwnProperty(script_name)) {
        _rmod.injectScript(script_name, uri,
            _rmod.requireCallback,
                _rmod.requirePrepare);
    }
};

var ready = function(fn) {
    _rmod.on_ready_fn_stack.push(fn);
};



Most of solutions shown here imply dynamical loading. I was searching instead for a compiler which assemble all the depended files into a single output file. The same as Less/Sass preprocessors deal with the CSS @import at-rule. Since I didn't find anything decent of this sort, I wrote a simple tool solving the issue.

So here is the compiler, https://github.com/dsheiko/jsic, which replaces $import("file-path") with the requested file content securely. Here is the corresponding Grunt plugin: https://github.com/dsheiko/grunt-jsic.

On the jQuery master branch, they simply concatenate atomic source files into a single one starting with intro.js and ending with outtro.js. That doesn't suits me as it provides no flexibility on the source code design. Check out how it works with jsic:

src/main.js

var foo = $import("./Form/Input/Tel");

src/Form/Input/Tel.js

function() {
    return {
          prop: "",
          method: function(){}
    }
}

Now we can run the compiler:

node jsic.js src/main.js build/mail.js

And get the combined file

build/main.js

var foo = function() {
    return {
          prop: "",
          method: function(){}
    }
};



This is perhaps the biggest weakness of JavaScript in my opinion. It's caused me no end of problems over the years with dependency tracing. Anyhow, it does appear that the only practical solution is to use script includes in the HTML file and thus horribly making your JavaScript code dependent upon the user including the source you need and making reuse unfriendly.

Sorry if this comes across as a lecture ;) It's a (bad) habit of mine, but I want to make this point.

The problem comes back to the same as everything else with the web, the history of JavaScript. It really wasn't designed to be used in the widespread manner it's used in today. Netscape made a language that would allow you to control a few things, but they didn't envisage its widespread use for so many things as it is put to now and for one reason or another it's expanded from there, without addressing some of the fundamental weaknesses of the original strategy.

It's not alone of course. HTML wasn't designed for the modern webpage; it was designed to be a way of expressing the logic of a document, so that readers (browsers in the modern world) could display this in an applicable form that was within the capabilities of the system, and it took years for a solution (other than the hacks of MS and Netscape) to come along. CSS solves this problem, but it was a long time coming and even longer to get people to use it rather than the established BAD techniques. It happened though, praise be.

Hopefully JavaScript (especially now it's part of the standard) will develop to take on board the concept of proper modularity (as well as some other things) as every other (extant) programming language in the world does and this stupidity will go away. Until then you just have to not like it and lump it, I'm afraid.




I had a simple issue, but I was baffled by responses to this question.

I had to use a variable (myVar1) defined in one JavaScript file (myvariables.js) in another JavaScript file (main.js).

For this I did as below:

Loaded the JavaScript code in the HTML file, in the correct order, myvariables.js first, then main.js:

<html>
    <body onload="bodyReady();" >

        <script src="myvariables.js" > </script>
        <script src="main.js" > </script>

        <!-- Some other code -->
    </body>
</html>

File: myvariables.js

var myVar1 = "I am variable from myvariables.js";

File: main.js

// ...
function bodyReady() {
    // ...
    alert (myVar1);    // This shows "I am variable from myvariables.js", which I needed
    // ...
}
// ...

As you saw, I had use a variable in one JavaScript file in another JavaScript file, but I didn't need to include one in another. I just needed to ensure that the first JavaScript file loaded before the second JavaScript file, and, the first JavaScript file's variables are accessible in the second JavaScript file, automatically.

This saved my day. I hope this helps.




Or rather than including at run time, use a script to concatenate prior to upload.

I use Sprockets (I don't know if there are others). You build your JavaScript code in separate files and include comments that are processed by the Sprockets engine as includes. For development you can include files sequentially, then for production to merge them...

See also:




I just wrote this JavaScript code (using Prototype for DOM manipulation):

var require = (function() {
    var _required = {};
    return (function(url, callback) {
        if (typeof url == 'object') {
            // We've (hopefully) got an array: time to chain!
            if (url.length > 1) {
                // Load the nth file as soon as everything up to the
                // n-1th one is done.
                require(url.slice(0, url.length - 1), function() {
                    require(url[url.length - 1], callback);
                });
            } else if (url.length == 1) {
                require(url[0], callback);
            }
            return;
        }
        if (typeof _required[url] == 'undefined') {
            // Haven't loaded this URL yet; gogogo!
            _required[url] = [];

            var script = new Element('script', {
                src: url,
                type: 'text/javascript'
            });
            script.observe('load', function() {
                console.log("script " + url + " loaded.");
                _required[url].each(function(cb) {
                    cb.call(); // TODO: does this execute in the right context?
                });
                _required[url] = true;
            });

            $$('head')[0].insert(script);
        } else if (typeof _required[url] == 'boolean') {
            // We already loaded the thing, so go ahead.
            if (callback) {
                callback.call();
            }
            return;
        }

        if (callback) {
            _required[url].push(callback);
        }
    });
})();

Usage:

<script src="prototype.js"></script>
<script src="require.js"></script>
<script>
    require(['foo.js','bar.js'], function () {
        /* Use foo.js and bar.js here */
    });
</script>

Gist: http://gist.github.com/284442.




In modern language it would be

function loadJs( url ){
  return new Promise( resolve => {
    const script = document.createElement( "script" );
    script.src = url;
    script.onload = resolve;
    document.head.appendChild( script );
  });
}



var js = document.createElement("script");

js.type = "text/javascript";
js.src = jsFilePath;

document.body.appendChild(js);



This should do:

xhr = new XMLHttpRequest();
xhr.open("GET", "/soap/ajax/11.0/connection.js", false);
xhr.send();
eval(xhr.responseText);



Maybe you can use this function that I found on this page How do I include a JavaScript file in a JavaScript file?:

function include(filename)
{
    var head = document.getElementsByTagName('head')[0];

    var script = document.createElement('script');
    script.src = filename;
    script.type = 'text/javascript';

    head.appendChild(script)
}



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