knockout.js - 在订阅同一可观察值时获取可观察值的前一个值

Question

在 knockout 中，在接收新值之前，是否可以在该可观察值的订阅中获取该可观察值的当前值？

示例:

this.myObservable = ko.observable();
this.myObservable.subscribe(function(newValue){
    //I'd like to get the previous value of 'myObservable' here before it's set to newValue
});

Answer 1

ko.subscribable.fn.subscribeChanged = function (callback) {
    var oldValue;
    this.subscribe(function (_oldValue) {
        oldValue = _oldValue;
    }, this, 'beforeChange');

    this.subscribe(function (newValue) {
        callback(newValue, oldValue);
    });
};

像这样使用上面的内容:

MyViewModel.MyObservableProperty.subscribeChanged(function (newValue, oldValue) {

});