How can I return an array of promises in a then statement

问题

So for the past few hours I've been looking into async stuff and using promises. I'm using the testing framework protractor, and theres a few async things I'm having trouble with.

In this save function, I call cm.org1.all() asynchronously, and use then to get the response. I loop over the response, and I need call getNewElement() to each element in the response, which also has an async call in it, so each returns a promise.

So I have this array of promises, but I don't know how to return it. The return of cm.save() is []. I need it to be ['foo',foo',foo',foo']

This code below doesn't work, but it's what I have so far.

 var cm = companyManagement() {
    //whatever is initialized below is initialized up here

    this.save = function() {
        cm.saveButton.click(); 
        var elements;
        var promises = [];
        var defer = protractor.promise.defer();
        cm.org1.all(by.repeater('brand in vm.brands'))
        .then(function(response) {
            //elements is of length 4
            elements = response;
            for(var i=0; i<elements.length;i++) {
                promises.push(getNewElement(elements, i));
            }
            //defer.fulfill(promises); not correct?
        });
        return protractor.promise.all(promises); //not correct?
    };

    function getNewElement(elements, i) {
         var defer = protractor.promise.defer();
        var alias = elements[i].element(by.binding('brand.alias'));
        alias.getText().then(function(aliasText) {
            defer.fulfill('foo');
        });
        return defer.promise;
    }
}
    cm.save()
    .then(function(response){
       console.log("my new array is",response);
    });

回答1:

Dealing with protractor promises manually in your tests is usually a sign of overcomplicating a problem. Protractor has a variety of abstractions and functional programming tools that cover most of the use cases.

You can solve it in just a single line if you would use repeater's .column():

this.save = function() {
    cm.saveButton.click(); 
    return cm.org1.all(by.repeater('brand in vm.brands').column('brand.alias')).getText();
};

---

I would do this, but I want to eventually be able to get the element's parent, if the column brand.alias matches with a certain constant I have. if I only have the alias text I couldn't be able to get the parent, correct me if I'm wrong.

filter() and map() to the rescue:

cm.org1.all(by.repeater('brand in vm.brands').column('brand.alias')).filter(alias) {
    return alias.getText().then(function (aliasText) {
        return aliasText === "foo";
    });
}).map(function (alias) {
    return alias.element(by.xpath("..")).getText();  // getting the parent
});

回答2:

Try:

this.save = function() {
    cm.saveButton.click(); 
    var elements;
    var promises = [];
    var defer = protractor.promise.defer();
    return cm.org1.all(by.repeater('brand in vm.brands'))
    .then(function(response) {
        //elements is of length 4
        elements = response;
        for(var i=0; i<elements.length;i++) {
            promises.push(getNewElement(elements, i));
        }
        return protractor.promise.all(promises);
    });
};

来源：https://stackoverflow.com/questions/33921760/how-can-i-return-an-array-of-promises-in-a-then-statement