/**
 * require
 * @author Heekei
 * @version 0.2.1
 * 
 * @description 異步加載外部js,可回調(diào)
 * @param {Object} setting 配置項(xiàng)
 * @param {Object=} setting.depends 依賴文件數(shù)組，可選
 * @param {String} setting.url  外部js地址
 * @param {Function=} setting.callback 回調(diào)函數(shù)，可選
 * @param {Boolean=} setting.defer  是否在DomContentLoaded之前運(yùn)行，默認(rèn)為false（注：如果depends具有強(qiáng)依賴性，請(qǐng)將defer設(shè)置為true）
 */
var require = function (setting) {
    var _this = this;
    if (require.loaded.indexOf(setting.url) !== -1) return;
    require[setting.url] = {};
    require[setting.url].Timer = null;
    // 加載依賴文件
    if (setting.depends) {
        // 標(biāo)記依賴文件正在加載
        require[setting.url].dependsLoading = true;

        // 檢查依賴文件是否已經(jīng)加載過(guò)
        for (var x in setting.depends) {
            if (require.loaded.indexOf(setting.depends[x]) !== -1) {
                setting.depends.splice(x, 1)
            }
        }

        // 記錄正在加載的依賴到數(shù)組【加載中的依賴】
        require[setting.url].loadingDepends = setting.depends;

        // 設(shè)置主JS的依賴文件的長(zhǎng)度
        require[setting.url].dLen = setting.depends.length;

        // 定時(shí)檢查依賴是否加載完畢
        require[setting.url].Timer = setInterval(function () {
            if (require[setting.url].dependsLoading === false) { // 依賴文件加載完畢
                // 加載主JS
                require({
                    url: setting.url,
                    callback: setting.callback
                })
                clearInterval(require[setting.url].Timer) // 清除定時(shí)器
            }
        }, 0)

        // 循環(huán)加載依賴文件
        for (var d = 0; d < require[setting.url].dLen; d++) {
            require({
                url: setting.depends[d],
                callback: function () {
                    // 加載完成后，將該依賴文件從【加載中的依賴】數(shù)組中刪除
                    require[setting.url].loadingDepends.splice(require[setting.url].loadingDepends.indexOf(this.url), 1)

                    // 如果【加載中的依賴】為空，將“依賴加載中”的狀態(tài)標(biāo)記為false
                    if (require[setting.url].loadingDepends.length == 0) require[setting.url].dependsLoading = false;
                }
            })

        }

        // 退出函數(shù)，保證主JS在加載依賴文件的過(guò)程中不進(jìn)行加載
        return;
    }

    var script = document.createElement("script"); // 加載JS文件

    // 觸發(fā)回調(diào)
    if (script.readyState) { //IE 
        script.onreadystatechange = function () {
            if (script.readyState == "loaded" ||
                script.readyState == "complete") {
                script.onreadystatechange = null;
                console.log(setting.url + " has loaded");
                isLoaded = true;
                if (typeof setting.callback === "function") {
                    setting.callback();
                }
            }
        };
    } else { //Others 
        script.onload = function () {
            console.log(setting.url + " has loaded");
            if (typeof setting.callback === "function") {
                setting.callback();
            }
        };
    }

    script.src = setting.url + "?" + Math.random();

    if (setting.defer) {
        script.defer = "defer";
    }
    require.loaded.push(setting.url);
    document.head.appendChild(script);
}
require.loaded = []