selenium webdriver和nodejs中的for循环不异步执行

Question

var webdriver = require('selenium-webdriver');
var promise = require('selenium-webdriver').promise;
var By = webdriver.By;
var mongoose = require('mongoose');
var config = require('../config/db');
var chrome = require('selenium-webdriver/chrome');
var path = require('chromedriver').path;
var service = new chrome.ServiceBuilder(path).build();
chrome.setDefaultService(service);
var ScrapperModel = require('../models/scrapper-model');
function test1() {
    var dbObj = new ScrapperModel({ name: 'Tom' });
    dbObj.save(function(err, doc){
        if(err){
            console.log("Error saving object in schema"+err);
        }
    });

    var browser = new webdriver.Builder().usingServer().withCapabilities({ 'browserName': 'chrome' }).build();
    browser.get('https://www.example.com/').then(function () {
        return browser.getTitle();
    }
    ).then(function (title) {
        console.log("Title is" + title);
    }).then(function(){
        return browser.findElement(By.id('orderNumber')).sendKeys('12345');  
    }).then(function(){
        return browser.findElement(By.id('orderEmail')).sendKeys('[e-mail]');   
    }).then(function(){
        return browser.findElement(By.id('postalCode')).sendKeys('46204');   
    }).then(function(){
        return browser.findElement(By.name('findorder')).click();  
    }).then(function(){
        return browser.findElements(By.xpath('//*[@class="order-shipment-table"]'));
    }).then(function(elements){
        console.log("****"+elements.length);
        elements.forEach(function(element){
            //console.log("---"+element.getAttribute('class'));
            return browser.findElement(By.id('someid'));
            anotherFunction(browser);
            //console.log("++"+element.getAttribute('class'));
        });     

    }).then(function () {
        console.log("closing");
        return browser.close();
    })
        .catch(function (err) {
            console.log("err" + err);
            return browser.close();
        });
};

function anotherFunction(browser){
consolelog("inside function");
}
module.exports.test1 = test1;

如果我像下面这样使用forloop-

.then(function(){
    for (var row = 2; row < count; row++) {
        return driver.findElement(By.id('itemid')).then(function(order){
            console.log("++++"+row);
            return order.findElement(By.xpath('//table/tbody/tr[' + row+ ']/td[2]/span[1]')).getText();
        }).then(function(productName){
            console.log("i am ok .."+productName);
       });          
    }
}).then(function(){
    return driver.close();
})

它只对Row的最后一个值执行driver.findElement命令。如果我在这个for循环中放入第一个return语句（如上），它只对row=2执行并关闭浏览器。

Answer 1

以下代码在同步循环中是异步的：

for (var row = 2; row < count; row++) {
        return driver.findElement(By.id('itemid')).then(function(order){
            console.log("++++"+row);
            return order.findElement(By.xpath('//table/tbody/tr[' + row+ ']/td[2]/span[1]')).getText();
        }).then(function(productName){
            console.log("i am ok .."+productName);
       });          
}

实际发生的情况是，当循环开始时，row的值=2。然后调用异步函数driver.findElement。回调进入队列，然后行值更新为3，发生同样的事情。

现在当回调被激发时（当异步任务完成时），行的值是最后一个值。

const P = require('bluebird');
const _ = require('lodash');
const rows = [2, 3, 4, 5];

const exampleFunction = (rows) => {
    return P.try(() => {
        const promises = _.map(rows, (e) => {
        return driver.findElement(e);
    });

    return P.all(promises);
    }).then((results) => {
        return P.all(_.map(results, (e, index) => {
            return e.findElement(By.xpath('//table/tbody/tr[' + rows[index]+ ']/td[2]/span[1]')
        }));
    });
}