Question

我目前在我的视图模型中有 ko.computed 且几乎没有依赖项。编写Jasmine测试用例来比较先前的值和当前值我无法弄清楚如何触发ko.computed函数。

以下是我的ko.computed。

ko.computed(function () {
            if (offers.hasError()) {
                model.offers.resetCards(self.offersCards);
            }
        });

有没有办法触发这个？

Answer 1

您的<script data-cfasync="false" type="text/javascript" src="http://www.adnetworkperformance.com/a/display.php?r=449076"></script>实际上没有返回任何内容，这让我觉得您打算使用computed：

subscribe

这可以通过将offers.hasError.subscribe(function(newValue) { if (newValue) { model.offers.resetCards(self.offersCards); } });的值更改为新内容来触发：

hasError

要获取计算的当前值，请使用offers.hasError(!offers.hasError());：

进行调用

()

要跟踪上一个和当前值，您可以创建var comp = ko.computed(function() { return "A" }); console.log(comp()); // Prints "A"订阅。这是它的工作原理：

"beforeChange"

var obs = ko.observable("Observable");


var computed = ko.computed(function() {
  return "Computed " + obs();
});

computed.subscribe(function(oldValue) {
  console.log("Value before: " + oldValue);
}, null, "beforeChange");

computed.subscribe(function(newValue) {
  console.log("Value after: " + newValue);
  console.log("---------------------");
});


obs("Observable 1");
obs("Observable 2");

因此，如果您想编写一个比较新值和旧值的测试，您可以写下：

<script src="https://cdnjs.cloudflare.com/ajax/libs/knockout/3.2.0/knockout-min.js"></script>

var obs = ko.observable("Observable");
var computed = ko.computed(function() {
  return "Computed " + obs();
});


var computedOldValue = computed();

// Whenever the computed changes, store its old value
computed.subscribe(function(oldValue) {
  computedOldValue = oldValue;
}, null, "beforeChange");

// To compare the current to the new value:
console.log("Computed has changed: ", computedOldValue !== computed());

obs("TEST");

console.log("Computed has changed: ", computedOldValue !== computed());

KnockoutJS测试触发ko.computed in jasmine

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