使用JSON处理时，剔除计算对象不起作用

Question

I am new to Knockout, The problem is that I try to load object from JSON and also use computed value please see jsfiddle example and tell me what I am doing wrong it should display "Hello World" + "start date" (in the third line) http://jsfiddle.net/qp86wbdt/3/

self.starttextt= ko.computed(function() {
    return  " Hello world " + this.start();
}, this);             

it may worth mentioning that this computed object lives in "events" object (which is loaded from json) while "events" object live in the ViewModel object.

Appreciate your help, thanks

Answer 1

You have quite some problems with your current approach:

You need to fix your Event function to take some parameter to fill in with data:

 function Event(data) {
     var self = this;
     self.title = ko.observable(data.title);
     self.start = ko.observable(data.start);
     self.starttextt = ko.computed(function () {
         return " Hello world " + this.start();
     }, this);
 }

Then writing var data = [Event]; just create an array with the Event function and it does not do any kind of mapping. You need to call map on your objs array:

 var objs = JSON.parse(js);
 var data = objs.map(function (e) {
     return new Event(e)
 });

And you need to use data in your viewModel instead of obj

 var viewModel = function () {
     var self = this;
     self.events = ko.observableArray(data);
 };

Demo JSFiddle .

However you don't need to write all these mapping code because there is already a plugin exists called Mapping plugin which is built to handle these kind of situations.

Here is your sample rewritten with the mapping plugin:

 var mapping = {
     create: function (options) {
         var event = ko.mapping.fromJS(options.data);
         event.starttextt = ko.computed(function () {
             return " Hello world " + event.start();
         }, event);
         return event;
     }
 }
 var viewModel = function () {
     var self = this;
     self.events = ko.mapping.fromJSON(js, mapping);
 };

Demo JSFiddle .