設置js加載順序

如果在一個頁面引入多個js,不會按寫的順寫加載，有時會發現函數未定義，我們可以在一個js中動態添加script

var arr =["a.js","b.js",.....];
loadScripts(arr);//執行加載
function loadScripts(arr){
    var index=0;
    function  callback(){
        if(arr[++index]){
            loadSingleScript(arr[index],callback)
        }
    }
    loadSingleScript(arr[index],callback);
};

function loadSingleScript(url, callback) {
    var script = document.createElement('script');
    script.type = 'text/javascript';
    if (callback)
        script.onload = script.onreadystatechange = function() {
            if (script.readyState && script.readyState != 'loaded' && script.readyState != 'complete')
                return;
            script.onreadystatechange = script.onload = null;
            callback();
        };
    script.src = url;
    document.getElementsByTagName('head')[0].appendChild (script);
}