Knockout ko.utils.arrayFirst总是返回null

Question

我无法弄清楚为什么它总是返回null。即使文本框值具有新值。

   self.update = function (data, event) {
        if (event.keyCode === 13 || event.type === "blur") {
            console.log(self.getPercentById(event.target.value)); // always null
        }
        return true;
    };
    self.getPercentById = function (percent) {
        return ko.utils.arrayFirst(self.List(), function (item) {
            return item.Percent() === percent;
        });
    };

视图模型

    function ViewModel() {
        var self = this;
        self.url = ko.observable(document.URL.substr(document.URL.lastIndexOf('/') + 1));
        self.activeSort = ko.observable();
        self.sortColumn = null;
        self.selected = ko.observableArray()(false);
        self.allSelected = ko.observable(false);
        self.selectedItem = ko.observable(null);
        self.List = ko.observableArray();
        self.sort = function (items, event) {
...