Selenium和异步JavaScript调用 [英] Selenium and asynchronous JavaScript calls

问题描述

我对Selenium和JavaScript回调函数都很陌生，我有一个很大的问题，我无法自己解决。我需要使用JavaScript的指定变量。如果我使用GoogleChrome打开页面并使用控制台输入我的JavaScript代码，我可以使用以下内容获取变量：

i'm quite new to Selenium and JavaScript-callback functions and i have a big issue I can't solve myself. I need a specified variable using JavaScript. If I open the page with GoogleChrome and use the console to enter my JavaScript-Code I can get the variable using something like this:

1. var myId;
2. getSomeIdStuffInfo("somestuff",function(docId)(myId = docId));
3. return myId;

如果我一步一步地输入这一行，我很容易得到正确的值myId。但是，当然，如果我尽可能快地执行三行，我得到null作为返回值，因为当我返回myId时回调函数没有完成。 SOOOO ..如果我像这样使用selenium：

If I enter this lines step by step I easily get the correct value myId. But, of course, if i execute the three lines as fast as possible, i get null as return value because the callback function is not finished when i return myId. SOOOO.. if I use selenium like this:

JavascriptExecutor js = (JavascriptExecutor) driver; 
    String docInfoVal = (String) js.executeScript("" +
            "var myId; " +
            "getCurrentDocumentInfo(\"somestuff\"," +
                "function(docId) {" +
                    "myId = docId;" +
                "}" +
            ");" +
            "return myId;");

我只得到null作为结果。所以...不知何故，我必须等待回调函数，直到我返回myId。我是否必须使用executeAsyncScript以及如何使用？我坐了几个小时，尝试了不同的东西，但我找不到答案。

I only get null as result. So... somehow I have to "wait" for the callback function until i return myId. Do I have to use executeAsyncScript and how? I'm sitting on it for hours and tried different things but I just can't find the answer.

提前感谢您的帮助！

推荐答案

对于异步代码你必须使用 executeAsyncScript ：

For asynchronous code you have to use executeAsyncScript:

JavascriptExecutor js = (JavascriptExecutor) driver; 
String docInfoVal = (String) js.executeAsyncScript("" +
        "var done = arguments[0]; " +
        "getCurrentDocumentInfo(\"somestuff\"," +
            "function(docId) {" +
                "done(docId);" +
            "}" +
        ");");

使用 executeAsyncScript 调用的脚本将具有一个回调添加到传递给它的参数列表中。由于您没有向脚本传递任何参数，因此 arguments [0] 包含回调。您的代码必须在完成工作后调用此回调。您为回调赋予的值是 executeAsyncScript 返回的值。

The script you call with executeAsyncScript will have a callback added to the list of arguments passed to it. Since you pass no arguments to your script, then arguments[0] contains the callback. Your code must call this callback when it is done working. The value you give to the callback is the value that executeAsyncScript returns.

在上面的代码中，我是通过将其置于匿名函数中来拼写对 done 的调用，但代码可以更简洁地编写为：

In the code above, I've spelled out the call to done by putting it in an anonymous function but the code could be written more concisely as:

JavascriptExecutor js = (JavascriptExecutor) driver; 
String docInfoVal = (String) js.executeAsyncScript("" +
        "var done = arguments[0]; " +
        "getCurrentDocumentInfo(\"somestuff\", done);");

甚至：

JavascriptExecutor js = (JavascriptExecutor) driver; 
String docInfoVal = (String) js.executeAsyncScript(
        "getCurrentDocumentInfo('somestuff', arguments[0]);");

这篇关于Selenium和异步JavaScript调用的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！