动态加载JavaScript文件

Question

I am trying to load a list of js files dynamically. Everything for the moment works fine. The only problem is that I wrote my func inside the loop so my code will be repeated many times. What I want to do is to make a loop to download the files and then confirm that they are already loaded and executed my func() .

For my code if I write func() outside the loop I get an error message. Mean outside onreadystate etc I get error message

   function( libs, func ){
            if( typeof func === 'function' ) {


                libs.forEach( function( fileName ) {

                    var script = document.createElement('script');
                    var head   = (document.getElementsByTagName("head")[0] || document.documentElement);
                    script.setAttribute("type", "text/javascript");

                    if (script.readyState){  //IE
                        script.onreadystatechange = function(){
                            if (script.readyState == "loaded" || script.readyState == "complete") {
                                script.onreadystatechange = null;
                                head.remove( script );
                                func();
                            }
                        };
                    } else {  //Others browsers
                        script.onload = function(){
                            head.remove( script );
                            loaded = true;
                            func();
                        };
                    }
                    script.setAttribute("src", fileName);
                    head.appendChild( script );

                });


            }
        }

Answer 1

do you realy need to load it by your own function? Why don't you use a script loader like requirejs?

Here you can find other: https://stackoverflow.com/questions/12779565/comparing-popular-script-loaders-yepnope-requirejs-labjs-and-headjs

Answer 2

I'm not exactly sure that I understand correctly, but you want to execute your function when all files are downloaded? The most common way would be to have a counter. I used this function when doing something similar, which takes a function that can be executed after each file load, and one that is executed when all files are loaded.

I used the following function to keep track of the number of files loaded.

function loadJs(files, perFileCallback, doneCallback){
    var numFiles = files.length,
        numFilesLoaded = 0,
        loadedFiles = [],
        fileOrder = {};

    if(numFiles === 0){
        doneCallback([]);
        return;
    }

    function _loadFileCallback (file, fileName) {
        numFilesLoaded++;
        loadedFiles[fileOrder[fileName]] = file; // Must be placed in correct order.
        perFileCallback(numFilesLoaded);
        if (numFiles === numFilesLoaded && perFileCallback) {
            doneCallback(loadedFiles);
        }
    }

    for (var i = 0; i < files.length; i++) {
        fileOrder[files[i]] = i;
        _loadFile(files[i], _loadFileCallback); // Load the file with ajax and perform _loadFileCallback when done.
    }
}

You can also see all three functions I chained to use it on pastebin .

It uses jQuery, but you can swap it with a normal ajax call if you desire.

This also takes into account that when adding the files to your head, you do it in the correct order. This was because I would have a file which defined var app, and one which defined app.mySite, and it was vital that app was defined before app.mySite could be created.