Selenium and JavaScript Asynchronous Calls
I am completely new to Selenium and JavaScript-callback functions and I have a big problem that I cannot solve on my own. I need the 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;
If I enter these lines step by step, I can easily get the correct myId value. But of course, if I execute three lines as quickly as possible, I get null as the return value, because the callback is not complete 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;");
I am getting null as result. So ... for some reason I need to "wait" for the callback function until I return myId. Should I use executeAsyncScript and how? I've been sitting on it for hours and trying different things, but I just can't seem to find the answer.
Thanks in advance for your help!
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For asynchronous code, you should use executeAsyncScript
:
JavascriptExecutor js = (JavascriptExecutor) driver;
String docInfoVal = (String) js.executeAsyncScript("" +
"var done = arguments[0]; " +
"getCurrentDocumentInfo(\"somestuff\"," +
"function(docId) {" +
"done(docId);" +
"}" +
");");
A script called with executeAsyncScript
will have a callback added to the list of arguments passed to it. Since you are not passing arguments to your script, it arguments[0]
contains a callback. Your code should call this callback when it works. The value you give the callback is the return value executeAsyncScript
.
In the above code, I wrote the call done
by placing it in an anonymous function, but the code could be written more concisely:
JavascriptExecutor js = (JavascriptExecutor) driver;
String docInfoVal = (String) js.executeAsyncScript("" +
"var done = arguments[0]; " +
"getCurrentDocumentInfo(\"somestuff\", done);");
Or even:
JavascriptExecutor js = (JavascriptExecutor) driver;
String docInfoVal = (String) js.executeAsyncScript(
"getCurrentDocumentInfo('somestuff', arguments[0]);");
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Although it's pretty much the same as @Louis. You need to be installed in advance setScriptTimeout
to pass the script.
The default timeout for a script to be executed is 0ms. In most cases, including the examples below, you need to set the scriptWebDriver.Timeouts.setScriptTimeout (long, java.util.concurrent.TimeUnit) timeout in advance to a value large enough.
Below is an example for which I wait 10 seconds to return a string
driver.manage().timeouts().setScriptTimeout(20, TimeUnit.SECONDS);//important
JavascriptExecutor executor = (JavascriptExecutor) driver;
String val = (String) executor.executeAsyncScript(""
+ "var done=arguments[0]; "
+ "setTimeout(function() {"
+ " done('tada');"
+ " }, 10000);");
System.out.println(val);
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