从淘汰表的选择列表中选择项目时，值对象未更新

Question

I'm having some problems with the value binding on a select tag in knockout.

I've got the following markup:

<select id="faultCode" data-bind="options: FaultCodes, optionsText: 'Description', value: FaultCode, optionsCaption: 'Choose a Fault Code'"></select>
<select id="causeCode" data-bind="options: CauseCodes, optionsText: 'Description', value: CauseCode, optionsCaption: 'Choose a Cause Code'"></select>
<select id="serviceAction" data-bind="options: ActionCodes, value: ActionCode, optionsText: 'Description', optionsCaption: 'Choose an Action Code'"></select>
<select id="plantClass" data-bind="options: PlantClasses, value: PlantClass, optionsText: 'Description', optionsCaption: 'Choose a Plant Class'"></select>
<select id="plantItem" data-bind="options: PlantItems, value: PlantItem, optionsText: 'Description', optionsCaption: 'Choose a Plant Item'"></select>

And my Javascript:

self.FaultCode = ko.observable();
self.ActionCode = ko.observable();
self.PlantClass = ko.observable();
self.PlantItem = ko.observable();
self.CauseCode = ko.observable();

self.FaultCodes = ko.observableArray();
self.ActionCodes = ko.observableArray();
self.PlantClasses = ko.observableArray();
self.PlantItems = ko.observableArray();
self.CauseCodes = ko.observableArray();

self.closeRequest = function () {
    var fault = "";
    var action = "";
    var cause = "";
    var pc = "";
    var pi = "";
    if (self.FaultCode() != undefined) {
        fault = self.FaultCode();
    }
    if (self.ActionCode() != undefined) {
        action = self.ActionCode();
    }
    if (self.CauseCode() != undefined) {
        cause = self.CauseCode();
    }
    if (self.PlantClass() != undefined) {
        pc = self.PlantClass();
    }
    if (self.PlantItem() != undefined) {
        pi = self.PlantItem();
    }
}

If the user chooses an option from all 5 of the select boxes and fires the closeRequest function, the FaultCode observable has a value of "" (Empty String) and the CauseCode observable has a value of undefined. The three other value observables all have the correct object as their value.

Answer 1

Are you sure that your FaultCode has a value when you are entering closeRequest or whatever?

 console.log(self.FaultCode());

When you first get into that function. Also, you are saying if (self.FaultCode() != undefined) which is a loose comparison and not very good. If you are getting a value logged from the above console.log statement, this should fix it for you -

self.closeRequest = function () {
    console.log(self.FaultCode());
    var fault = "";
    var action = "";
    var cause = "";
    var pc = "";
    var pi = "";
    if (self.FaultCode()) {
        fault = self.FaultCode();
    }
    if (self.ActionCode()) {
        action = self.ActionCode();
    }
    if (self.CauseCode()) {
        cause = self.CauseCode();
    }
    if (self.PlantClass()) {
        pc = self.PlantClass();
    }
    if (self.PlantItem()) {
        pi = self.PlantItem();
    }
}

As long as the observables aren't false , undefined , "" , or null it will set fault equal to the observable.

When you use a double equal sign you are comparing the value loosely, use the triple equals for type comparison as well.