如何在我的对象范围之外调用'this'？

Question

我为网站开发了某种Jcrop初始化,我设法创建了自己的命名空间.我的问题是关于这个关键字.每次我都得来访问我的基本对象"APS"在任何回调函数,我必须换这个变量中(我选择了字说).有没有更好的方法呢？例如,我可以使用call或apply方法吗？这只是一个命名空间,所以我可以使用简单的aps.methodName但是为了这个例子,请不要介意.这是我的源代码:

var aps;

$(function(){
    aps = function(){

        //  private
        //  variables

        var bgColor = '#f5f5f5';
        var threshold = 370;
        var threshold_width = 800;

        return {
            tmpl                :       $('#jcrop-template').html(),
            upl_cont            :       {},
            form                :       {},
            logo_img            :       new Image(),
            jcrop_api           :       null,
            scaled_logo_url         :       '',
            image_filename          :       '',
            original_image_filename     :       '',
            mime                :       '',
            trueSize            :       '',

            jcrop_init          :       function (oiFrameRes){
                $('#logo_upload_form').find('img').hide();
                this.scaled_logo_url = oiFrameRes.image_url;
                this.logo_url = oiFrameRes.original_image_url;
                this.original_image_filename = oiFrameRes.original_image_filename;
                this.image_filename = oiFrameRes.image_filename;
                this.mime = oiFrameRes.mime;
                this.upl_cont = $('#facebox div#upload-container-d');
                this.logo_img = new Image();
                this.logo_img.that      =   this;
                this.logo_img.name      =   'logo';
                this.logo_img.onload    =   function(){
                    this.true_width=this.width;
                    this.true_height=this.height;
                    this.that.resize_image();
                    this.that.resize_facebox();
                    this.that.display_image();
                }
                this.logo_img.src = this.logo_url;
            },

            resize_image            :       function(){
                this.trueSize = '';
                if(typeof (this.oSettings.trueSize)!=='undefined') delete(this.oSettings.trueSize);
                if (this.logo_img.width > threshold){
                    if (this.logo_img.width > threshold_width){
                        this.trueSize = [ this.logo_img.width, this.logo_img.height ];
                        this.logo_img.height = this.logo_img.height / (this.logo_img.width / threshold_width);
                        this.logo_img.width = threshold_width;
                    }
                }
            },

            resize_facebox          :       function(){
                    var width = (this.logo_img.width > threshold) ? this.logo_img.width : threshold ;
                    $('#facebox').css({
                        left    :   $(window).width() / 2 - width / 2
                    }).
                    find('div.change-size').css({'width': width+30});
            },

            display_image : function (){
                if (this.jcrop_api === null) {
                    $logo_img = $(this.logo_img).css({'display':'block','margin-left':'auto','margin-right':'auto'})
                    if (this.upl_cont.find('#logo-container-d>img').length > 0){
                        if (this.upl_cont.find('#logo-container-d>img').attr('src').length > 0){
                            this.upl_cont.find('#logo-container-d').empty().append($logo_img);
                        }
                    }
                    else {
                        this.upl_cont.append(this.tmpl).find('#logo-container-d').append($logo_img);
                    }

                    var that = this;
                    if (typeof (this.upl_cont.find('#jcrop-menu1 a').data('events')) === 'undefined'){
                        this.upl_cont.find('#jcrop-menu1 a').click(function(){
                            if (this.href.indexOf('#crop')>-1){
                                $(this).closest('div').hide();
                                that.upl_cont.find('#jcrop-menu2').show();
                                that.setup_crop();
                            }
                            if (this.href.indexOf('#close')>-1){
                                manageIframeResponse();
                            }   
                            location.hash = '';
                            return false;
                        });
                    }
                }
                else {
                    this.reset();
                }
            },

            reset : function(){
                $('#jcrop-menu2',this.upl_cont).find('a').unbind('click').end().hide();
                $('#jcrop-coords-f',this.upl_cont).find('input[type="text"]').each(function(){this.value="";}).end().hide();
                $('#jcrop-menu1',this.upl_cont).find('a').unbind('click').end().show();
                this.jcrop_api.destroy();
                this.jcrop_api=null;
                this.display_image();
            },

            send_form : function (){
                var sPost = $(this.form).find('input[name="image_filename"]').val(this.image_filename).end()
                        .find('input[name="original_image_filename"]').val(this.original_image_filename).end()
                        .find('input[name="mime"]').val(this.mime).end()
                        .find('input[name="user_url"]').val($('#logo_upload_base_url').val()).end()
                        .find('input[name="user_key"]').val($('#logo_upload_user_key').val()).end()
                        .serialize();

                $.ajax({
                    url:'iframe_upload.php',
                    type:'POST',
                    data: sPost,
                    success : function(response){
                        manageIframeResponse();
                    },
                    dataType : 'json'
                });
            },

            setup_crop : function (){

                var that = this;
                if (this.jcrop_api === null) {
                    this.form = this.upl_cont.find('form#jcrop-coords-f').get(0);
                    this.upl_cont.find('#jcrop-menu2>a').click(function(){ that.send_form();return false; });
                    this.updateForm = function (){
                        var c = arguments[0];
                        that.form.x1.value=c.x;
                        that.form.x2.value=c.x2;
                        that.form.y1.value=c.y;
                        that.form.y2.value=c.y2;
                        that.form.h.value=c.h;
                        that.form.w.value=c.w;
                    }

                    this.oSettings.onSelect = this.updateForm;
                    if (typeof (this.trueSize) !== 'string' && $.isArray(this.trueSize)){
                        $.extend(this.oSettings,{'trueSize':this.trueSize});
                    }
                    $('#facebox #logo-container-d>img').Jcrop( this.oSettings, function(){

                        that.jcrop_api = this;
                        var _x1 = (that.logo_img.true_width*0.1).toFixed();
                        var _y1 = (that.logo_img.true_height*0.1).toFixed();
                        var _x2 = (that.logo_img.true_width*0.9).toFixed();
                        var _y2 = (that.logo_img.true_height*0.9).toFixed();
                        that.jcrop_api.setSelect([0,0,that.logo_img.true_width,that.logo_img.true_height]);
                        that.jcrop_api.animateTo([_x1,_y1,_x2,_y2]);
                    });
                }
            },

            updateForm : function (){},

            oSettings : {
                onSelect:'',
                onChange:'',
                keySupport: false,
                bgColor:bgColor,
                aspectRatio:1,
                minSize:[0,0]
            }
        }
    }();

    $(document).bind('afterClose.facebox', function() { 
        if (aps.jcrop_api !=null) {
            aps.jcrop_api.destroy();
            aps.jcrop_api=null;
        }
    });
});

Answer 1

无论何时使用函数调用*调用函数,该this值都将设置为全局变量(或undefined严格模式) - 即使从方法调用函数也是如此.道格拉斯·克罗克福德实际上已将此描述为该语言的一个缺陷.

将this值保存到函数可以访问的变量中是处理此问题的标准方法.

如果你真的想控制this你的回调中的内容,你可以使用apply或call.两者都将您想要this设置的第一个参数作为第一个参数.不同之处在于apply期望所有函数的参数都作为数组传递,同时call期望您单独列出它们.

因此,如果在你的ajax回调中,你想调用manageIframeResponse它,传递它ajax调用的响应(我知道你的例子没有传递响应,我只是说明你将如何做),并且它的this值是相同的作为当前对象,您可以这样做:

var self = this;
$.ajax({
    success : function(response){
        manageIframeResponse.apply(self, [response]); //<--- apply wants your arguments in array form
    }
});

或者,由于您的参数尚未采用数组形式,因此您可以更简单地使用 call

var self = this;
$.ajax({
    success : function(response){
        manageIframeResponse.call(self, response); //<---call takes the arguments listed out one at a time
    }
});

*有不同的方法来调用函数.

函数调用意味着您只是调用恰好位于当前范围内的函数:

foo() //inside foo, this will be the global object (or undefined in strict mode)

方法调用意味着您正在调用附加到对象的函数

myObj.foo() //inside foo, this will be myObj

这里有一个例子,如果你不小心的话,这会让你感到沮丧.

function objCreator() {
    var y = "There";

    function privateFunc() {
        alert(y); //alerts There as expected
        alert(this.someField); //undefined:  whoops - this is the global object, 
    }                          //so there's no someField 

    return {
        x: "Hi",
        someField: "blah",
        foo: function () {
            alert(this.x);
            privateFunc();
        }
    };
}