在量角器中传播承诺 [英] Spreading promises in Protractor

问题描述

q 库 有这个巧妙的功能来解析和传播多个承诺成单独的参数:

q library has this neat feature to resolve and spread multiple promises into separate arguments:

如果你有一个数组的承诺，你可以使用 spread 作为替换然后.扩展函数将值扩展"到履行处理程序的参数.

If you have a promise for an array, you can use spread as a replacement for then. The spread function "spreads" the values over the arguments of the fulfillment handler.

return getUsername()
    .then(function (username) {
        return [username, getUser(username)];
    })
    .spread(function (username, user) {

    });

在量角器中，我们尝试使用内置的protractor.promise 来自 WebDriverJS.

In protractor, we are trying to use the built-in protractor.promise coming from WebDriverJS.

问题:

是否可以使用 protractor.promise 实现传播"功能?

Is it possible to have the "spread" functionality with protractor.promise?

用例示例:

我们已经实现了一个自定义的 jasmine 匹配器来检查一个元素是否被聚焦.在这里，我们需要在进行相等比较之前解决两个 promise.目前，我们正在使用 protractor.promise.all() 和 then():

We've implemented a custom jasmine matcher to check if an element is focused. Here we need to resolve two promises before making an equality comparison. Currently, we are using protractor.promise.all() and then():

protractor.promise.all([
    elm.getId(),
    browser.driver.switchTo().activeElement().getId()
]).then(function (values) {
    jasmine.matchersUtil.equals(values[0], values[1]);
});

理想情况下，我们希望它处于更易读的状态:

which ideally we'd like to have in a more readable state:

protractor.promise.all([
    elm.getId(),
    browser.driver.switchTo().activeElement().getId()
]).spread(function (currentElementID, activeElementID) {
    return jasmine.matchersUtil.equals(currentElementID, activeElementID);
})

推荐答案

使用起来可能有点难看，但是你可以定义一个独立的辅助函数，可以传递给 then()作为参数并有一个回调，通常传递给 then() 传递给它.然后这个函数会将数组值转换为函数参数:

It may come a bit ugly to use, but you can define an independent helper function, which can be passed to then() as a parameter and have a callback, which is usually passed to then() to be passed to it. This function will then convert array value to function arguments:

protractor.promise.all([
    elm.getId(),
    browser.driver.switchTo().activeElement().getId()
]).then(spread(function (currentElementID, activeElementID) {
    // ---^^^----- use helper function to spread args
    jasmine.matchersUtil.equals(currentElementID, activeElementID);
}));


// helper function gets a callback
function spread(callback) {
    // and returns a new function which will be used by `then()`
    return function (array) {
        // with a result of calling callback via apply to spread array values
        return callback.apply(null, array);
    };
}

您仍然可以将其与另一个 then() 链接并提供拒绝回调；它保持量角器承诺的所有行为相同，但只是将值数组转换为参数.

You can still chain it with another then() and provide rejection callbacks; it keeps all the behavior of Protractor promises the same, but just converts array of values to arguments.

缺点是它在您的示例中看起来并不完美(不是 .all().spread() 而是 .all().then(spread()) ) 并且您可能必须为此助手创建一个模块或全局定义它，以便能够在多个测试文件中轻松使用它.

Drawbacks are that it is does not have a perfect look like in your example (not .all().spread() but .all().then(spread()) ) and you'll probably have to create a module for this helper or define it globally to be able to use it easily in multiple test files.

更新:

在 ES2015 中，可以使用 解构赋值 与 then() 一起:

With ES2015 it is possible to use destructuring assignment along with then():

protractor.promise.all([
    elm.getId(),
    browser.driver.switchTo().activeElement().getId()
]).then(function (values) {
    // Destructure values to separate variables
    const [currentElementID, activeElementID] = values; 
    jasmine.matchersUtil.equals(currentElementID, activeElementID);
}));

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