JavaScript对象文字嵌套对象状态

Question

I try to call "ViewModel.healthData.get" twice. In both cases, the method retrieves the data from the Internet. How can I make the "data" field retain its data?

function MyObject() {
    this.ViewModel.healthData.get(this.ViewModel.healthData.set);
}
MyObject.prototype = {
    ViewModel: {
        healthData: {
            data: null,
            set: function (result) {
                console.log("data from set");
                this.data = ko.mapping.fromJS(result);
            },
            get: function (callback) {
                if (this.data === null) {
                    $.ajax({
                        url: "/api/Health",
                        type: 'GET',
                        async: true,
                    }).done(callback);
                } else {
                    console.log("direct data");
                    return this.data;
                }
            }
        }
    }
};

Answer 1

I think you might want to have a look at Promises for this, it will simplify your workflow a lot. Since you are waiting for data to be populated, your calls could happen too soon or too late, but with promises that's not the case. Simply call resolve when done (or reject when failed) and pass it the data you received. From then on any function called with .then (and any function called that way since starting the request) will be called immediately with the data in the first argument.

function MyObject() {
    this.ViewModel.healthData = new Promise(function( resolve, reject ){
        $.ajax({
            url: "/api/Health",
            type: 'GET',
            async: true,
        }).done(function(data){ 
             resolve(ko.mapping.fromJS(result))
        }).fail( reject )
    });
}
MyObject.prototype = { ViewModel: { healthData: null } };

When you create a new MyObject here, it will automatically instantiate the required data inside a promise. To Access and use the data, simple use:

myInstanceOfMyObject.ViewModel.healthData.then(function(data){
    // Do whatever you want with the passed data here
});

This will resolve some of your asynchronous woes and highly simplify the structure.