在选择框中从任意 JavaScript 对象绑定选项值和选项文本

我可以绑定选项文本，但不能绑定选项值。这两个函数应该相同吗？

呈现的 HTML：（值在哪里？

<option value="">ROSSFORD D</option>

视图：

  <select multiple="multiple" width="75" id="foo" name="campaign[precincts][]" data-bind="options: campaign_precincts, optionsText: function(item) { 
                       return item.precinct_location.id 
                   }, optionsValue: function(foo) {return foo.precinct_location.id }> </select>

查看模型：

 var newCampaign = function() {
    this.items = ko.observableArray();
    this.freeText = ko.observable("");
    this.campaign_precincts = ko.observableArray();
    this.selectedPct = ko.observable();
    this.campaignName = ko.observable();
    this.userParty = ko.observable("");
    self = this;
    var question = this.freeText();
    this.searchMe = function() {
    console.log (self.userParty());
    self.items([]);
    self.userParty()
        if (this.freeText() != "") {
         // search by city
         $.getJSON('/search.json?q=' + this.freeText(), function (data) {
            if (data) {
              console.log(data)
              data.forEach(function(item) { self.items.push(item) })
            }
          });
        // search by zipcode
        $.getJSON('/search.json?z=' + this.freeText(), function (data) {
            if (data) {
              data.forEach(function(item) { self.items.push(item) })
            }
          });
        }
    }.bind(this); 
    this.addPrecinct = function(pct) {
      // returs false if pct is not a member of the array
      x = function(a,b){return!!~a.indexOf(b)}
      if ( x(self.campaign_precincts(),pct) == false) {
        self.campaign_precincts.push(pct);
      }; 
    }.bind(this);
    this.removePct = function() {
      self.campaign_precincts.pop(self.selectedPct());
    }
};
ko.applyBindings(new newCampaign());

js 对象：

data.precinct_location.city => "string"
data.precinct_location.id => 1234