Take elements while a condition evaluates to true (extending ElementArrayFinder)

Question

We have a menu represented as a ul->li list (simplified):

Answer 1

takewhile() actually worked for me once I removed the protractor.promise = require("q"); from onPrepare() - this was there to replace protractor.promise with q on the fly to be able to use the syntactic sugar like spread() function. Apparently, it is not safe to use q in place of protractor.promise.

All I have to do now is to add this to onPrepare():

protractor.ElementArrayFinder.prototype.takewhile = function(whileFn) {
    var self = this;
    var getWebElements = function() {
        return self.getWebElements().then(function(parentWebElements) {
            var list = [];
            parentWebElements.forEach(function(parentWebElement, index) {
                var elementFinder =
                    protractor.ElementFinder.fromWebElement_(self.ptor_, parentWebElement, self.locator_);

                list.push(whileFn(elementFinder, index));
            });
            return protractor.promise.all(list).then(function(resolvedList) {
                var filteredElementList = [];
                for (var index = 0; index < resolvedList.length; index++) {
                    if (!resolvedList[index]) {
                        break;
                    }
                    filteredElementList.push(parentWebElements[index])
                }
                return filteredElementList;
            });
        });
    };
    return new protractor.ElementArrayFinder(this.ptor_, getWebElements, this.locator_);
};

The usage is very similar to filter():

element.all(by.css("ul li a")).takewhile(function (elm) {
    return elm.getText().then(function (text) {
        return text;
    });
});

FYI, proposed to make takewhile() built-in.