For the W3C WebDriver "Find Element From Element" command, how does one format the element ID in request URL? - selenium

Question

I'm learning how a WebDriver works, and I don't understand how to format the request URL for Find Element From Element.
The element ID of Find Element will return something like this:
{"element-6066-11e4-a52e-4f735466cecf": "e72b0320-5d61-4886-b903-5b2e4bb43d88"}
As I understand it, the above {key: value} format IS the element ID. If that is the case, how does one user that as the {element id} in "POST /session/{session id}/element/{element id}/element"? If {key: value} IS NOT the element ID, what is? And what would a properly formatted request URL look like?
Thanks!

Answer 1

In the above example, the element ID is "e72b0320-5d61-4886-b903-5b2e4bb43d88". It's a bit confusing because rather than creating an object that looks like this:
{"ELEMENT": "e72b0320-5d61-4886-b903-5b2e4bb43d88"}
We have the very odd:
{"element-6066-11e4-a52e-4f735466cecf": "e72b0320-5d61-4886-b903-5b2e4bb43d88"}
What's going on here? It has been deemed from on high that the key which in a JSON object indicates that we are dealing with an element ID is the arbitrary and constant string "element-6066-11e4-a52e-4f735466cecf". The reason is that any non-arbitrary key might end up being a return value of some unrelated JavaScript code. Consider this JavaScript code:
return document.getElementById('foo');
This could be used in ExecuteScript as follows (for example in Python):
driver.execute_script("return document.getElementById('foo');");
What should be returned here? Well we are dealing with an actual HTML element, which can't be converted into JSON and sent back over the wire to the Python client. So instead, WebDriver stores a reference to that element as an ID, and sends that back. But it can't just send back the ID as a string, because there's no way for driver.execute_script to know in advance what sort of thing might be returned. Maybe it's not an element ID--maybe it's some other string related to your application. In the past, the standard format for a JSON WebElement was as I noted above (with the ELEMENT key).
At some point, however, someone must have written some JavaScript code which resulted in a JS object which contained the word ELEMENT as key somewhere inside. This object had nothing to do with WebElements, but when it was returned via a call to driver.execute_script, the client converted it into a WebElement object!
Whether or not this scenario ever actually happened is beside the point; the point is that a simple short word like ELEMENT is ripe for name clashes. The spec authors wanted a way to unambiguously denote that we are dealing with a WebElement even if we encounter it in a serialized JSON format, and in a way that is not likely to clash with other things web developers or testers are doing.
So the most direct answer to your question is, your POST request should look like:
POST /session/{session id}/element/e72b0320-5d61-4886-b903-5b2e4bb43d88/element