Selenium - check that an object is defined before using it

Question

I'm trying to perform testing using the selenium web driver, and part of this is waiting for my object to be defined on the page. NOTE: there is nothing in the DOM that will appear when my object is available and it is not an option to change that, so please don't suggest this. I need to check using the console.

Usually after a page is finished loading, I have to wait anywhere between 0-5 seconds for my object to exist, so the idea is to loop window.myObject !== undefined until it passes, at which point I'm sure that my object exists and I can call myObject.myFunctionCall(). If I don't perform this wait and just directly call myObject.myFunctionCall() after the page finishes loading, there's a good chance that I'll receive an error of myObject is not defined.

When I perform these steps from the console in my browser, it turns out perfectly fine:

let ret = false;
while (ret === false) {
    ret = window.myObject !== undefined;
    console.log(ret);
}
//now here ret has the value true. myObject is defined and I can continue with the test
myObject.myFunctionCall()
...

But then I try doing this with the selenium driver (this.driver) with the following code:

let ret = null;
while (ret === null) {
    let val = this.driver.executeScript("window.myObject !== undefined;"); //returns promise
    console.log(val);
    ret = await val; //await promise resolution and assign value to ret
    console.log(val);
    console.log(ret);
    //for some reason, ret is always null
}

which provides me with the following printout that repeats endlessly until the test fails on Error: function timed out, ensure the promise resolves within 30000 milliseconds:

Promise { <pending> }
Promise { null }
null
Promise { <pending> }
Promise { null }
null
Promise { <pending> }
Promise { null }
null
...

What am I missing here? Is there a better way to tell if my object is defined using the selenium web driver?

score 0 · Answer 1 · answered Jan 29 '20 at 21:38

I ended up with a structure like the following:

// Checks if myObject exists
const checkObjectDefined = () => window.myObject !== undefined;

let ObjectExists = false;
while (ObjectExists !== true) {
    ObjectExists = await this.driver.executeScript(checkObjectDefined);
    await this.driver.sleep(50);
}

//continue with test

With a caveat that if I move the checkObjectDefined definition to any other file and import it, it fails with the complaint InvalidArgumentError: invalid argument: 'script' must be a string.

Check this out:

I have a file helpers/myObject_helper.js that I want to put the definition in, but the following fails with the error InvalidArgumentError: invalid argument: 'script' must be a string:

helpers/myObject_helper.js:

// Checks if myObject exists
const checkObjectDefined = () => window.myObject !== undefined;

testcases/myObject_testcase.js:

const ObjectHelper = require('helpers/myObject_helper.js');

let ObjectExists = false;
while (ObjectExists !== true) {
    ObjectExists = await this.driver.executeScript(ObjectHelper.checkObjectDefined);
    await this.driver.sleep(50);
}

Selenium - check that an object is defined before using it

1 Answers1