使用另一个变量来初始化knockout observables

Question

我只是想知道为什么必须在下面的脚本中使用临时变量" that "(用当前分配的对象初始化,即" this "):

$(document).ready(function() {

    function ChatViewModel() {

        var that = this;

        that.userName = ko.observable('');
        that.chatContent = ko.observable('');
        that.message = ko.observable('');
        that.messageIndex = ko.observable(0);
        that.activePollingXhr = ko.observable(null);


        var keepPolling = false;

        that.joinChat = function() {
            if (that.userName().trim() != '') {
                keepPolling = true;
                pollForMessages();
            }
        }

        function pollForMessages() {
            if (!keepPolling) {
                return;
            }
            var form = $("#joinChatForm");


            that.activePollingXhr($.ajax({url: form.attr("action"), type: "GET", data: form.serialize(), cache: false,
                success: function(messages) {
                    console.log(messages);
                    for (var i = 0; i < messages.length; i++) {
                        that.chatContent(that.chatContent() + messages[i] + "\n");
                        that.messageIndex(that.messageIndex() + 1);
                    }
                },
                error: function(xhr) {
                    if (xhr.statusText != "abort" && xhr.status != 503) {
                        resetUI();
                        console.error("Unable to retrieve chat messages. Chat ended.");
                    }
                },
                complete: pollForMessages
            }));
            $('#message').focus();
        }

        that.postMessage = function() {
            if (that.message().trim() != '') {
                var form = $("#postMessageForm");
                $.ajax({url: form.attr("action"), type: "POST",
                    data: "message=[" + that.userName() + "] " + $("#postMessageForm input[name=message]").val(),
                    error: function(xhr) {
                        console.error("Error posting chat message: status=" + xhr.status + ", statusText=" + xhr.statusText);
                    }
                });
                that.message('');
            }
        }

        that.leaveChat = function() {
            that.activePollingXhr(null);
            resetUI();
            this.userName('');
        }

        function resetUI() {
            keepPolling = false;
            that.activePollingXhr(null);
            that.message('');
            that.messageIndex(0);
            that.chatContent('');
        }

    }

    //Activate knockout.js
    ko.applyBindings(new ChatViewModel());

});

为什么我不能只使用" 这个 "？有人可以解释一下吗？

Answer 1

this始终引用调用时范围内的对象,这可能会根据您的代码而改变.如果您希望它仍然是子函数中的对象,则将其分配给不会更改值的变量会解决此问题.