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Add popup based on class (most likely)

I'm trying to use Tampermonkey to add a popup on pages in the Canvas LMS. It's a forum, and after each post there is a "Reply" option, which is what I want to add the popup to. But when I click the "Reply" link, no popup appears. It opens the Reply box, as normal, but my popup is nowhere to be seen.
The code looks roughly like this:
<div class="entry-controls hide-if-collapsed hide-if-replying">
<div class="notification" data-bind="notification"></div>
<a role="button" class="discussion-reply-action entry-control" data-event="addReply" href="#">
<i class="icon-replied"></i>
<span aria-hidden="true">Reply</span>
<span class="screenreader-only">Reply to Comment</span>
</a>
</div>
The JS code I'm trying to add is:
document.querySelectorAll('.discussion-reply-action').forEach(item => {
item.addEventListener('click', event => {
alert("Popup text here");
})
})
In addition to .discussion-reply-action, I've tried using .entry-controls, .notification, .entry-control, even stuff like span[aria-hidden="true"]. Nothing seems to work.
I know the Tampermonkey script itself is applying correctly, because it has other functionality that is showing up as usual.
Any idea why this bit isn't working for me? I'm a complete JS noob, for what that's worth.

This got answered in the replies, but just wanted to formally note that it came down to delaying my code injection. I was trying to attach to elements that loaded after the doc. Once I got behind them, it worked fine.

How do I find the JavaScript referenced by this button?

Here is the "submit" button in the form with no onclick attribute.
<div id="243c0bb6-584e-4d48-a8fa-4308cd632028" class="nike-unite-submit-button joinSubmit nike-unite-component blurred">
<input id="d7e56d05-36e1-42f7-922b-d2979375007a" type="button" value="CREATE ACCOUNT">
</div>
I am more confused about the <form> tags from the Nike website source:
<form id="nike-unite-joinForm" class="nike-unite-form" method="post"
action="javascript:;" onsubmit="return false;">
...
</form>
How do I find out what is happening when I actually click the button on the page?
Using mouse-click breakpoints in chrome dev tools gives me a plethora of JavaScript functions takes too long for me to parse through.
If there are attributes or listeners added to the ID (such as a link to a script), I could not find them after using "Command-F" on the different attributes of the form.
The only other clue which I am not sure how to purse is that method="post".
I understand that all websites are different, but my question is a general one:
How do I figure out what the script that is being run when I click on the form?
Thanks in advance.

Try this:
document.getElementById('nike-unite-joinForm').submit();
This is from w3schools.com:
https://www.w3schools.com/jsref/met_form_submit.asp
EDIT:
Ok, I tried it myself on the registration website and it didn't work. Experimenting a bit with it I noticed an apparently random id is assigned to the DOM-Elements.
But I've found a solution:
document.getElementsByClassName("nike-unite-submit-button joinSubmit nike-unite-component")[0].children[0].click();
This works because the div in which the submit button is has a unique set of classes. So I get the first (and only) Element with this classes, and apply .click() to the first child element

Perhaps you could try to change submit with click:
document.getElementById('nike-unite-joinForm').click()

Can't click button with selenium

I'm a newcomer when it comes to javascript and selenium. I have created a simple add to cart project, but the one i am currently working on im having some troubles. The HTML code is:
<div class="buttons-set" id="shipping-method-buttons-container">
<button type="button" class="dark" onclick="shippingMethod.save()" onkeypress="shippingMethod.save()">Continue</button>
<span id="shipping-method-please-wait" class="please-wait icon icon--notch" style="display:none;">
Loading next step... </span>
</div>
I can't seem to figure out anyway where i can click the Continue button. I have tried things such as
driver.findElement(By.linkText("Continue")).click();
driver.findElement(By.xpath(//*[#id='shipping-method-buttons-container']/button)).click();
and many other combinations but none seemed to work.

Try getting the element by its class name:
driver.find_element_by_class_name("dark").click();

I believe you have used implicit wait. If not we need to add it.
driver.manage().timeouts().implicitlyWait(60, TimeUnit.SECONDS);
Also try this below xpath.
driver.findElement(By.xpath("//button[contains(text(),'Continue']")).click();
Hope this helps. Thanks.

Try this below code using cssSelector locator.
driver.findElement(By.cssSelector("button[class='dark'][type='button']")).click();
OR
Try to click the button using java-script executor.
WebElement continue_button = driver.findElement(By.cssSelector("button[class='dark'][type='button']"));
((JavascriptExecutor) driver).executeScript("arguments[0].click();", continue_button);

javascript execute button click event

I am new to javascript. Please find the below code for button,
<p class="actions">
<button class="button primary" type="submit">Login</button>
Sign Up
</p>
I need code to click this button. Anyone please help me. Thanks in advance.

Can you provide the rest of your code including the script section so we can see what you have there?
Basically however, if you just need the button to register a click I would change the button Id to an element since it's a unique element. Let's call it id =button1 . Then in your script section you would type
document.getElementById("button1").onclick=function(){
}
And type what you want to happen inside the {}

javascript change div html when click span

Ok I have a small question.
I have the following
<div><span class="spanright" onclick"">Update</span><label class="myinfo"><b>Business information:</b></label></div>
What I want to do is when the user clicks on the span it changes the html after the label an adds an input box and submit button.
I think I need to do a this.document but not sure

Hi hope this might give you a small understanding of what to do when it comes to registering events. StackOverflow is about you learning how to do something, so we dont write the scripts for you, we are just trying to point you in the right direction of it.
http://jsfiddle.net/WKWFZ/2/
I would recommend you to import jQuery library, as done in the example, if possible. It makes the the world of javascript alot easier!
Documentation to look up:
http://api.jquery.com/insertAfter/
http://api.jquery.com/bind/
Look up some jQuery tutorials! there is alot of them out there.

I added a form which will hold the input
JavaScript:
function showInput()
{
document.getElementById('container').innerHTML += '<input type="text"/><input type="submit"/>';
}
HTML:
<div id="container">
<span class="spanright" onclick"showInput()">Update</span>
<label class="myinfo"><b>Business information:</b></label>
</div>

Summoner's answer is right, but I prefer using jquery (it's loaded on almost every page I work with):
HTML:
<div id="container">
<span class="spanright">Update</span>
<label class="container"><b>Business information:</b></label>
</div>​
Javascript:
​$(".spanright").click(function(){
$("#container").append('<br /><input type="text"/><input type="submit"/>');
$(".spanright").unbind('click');
})​​;​
This way, the click event will work once, as it is what you probably intended.

Try this in jquery flavor --
$(document).ready(function(){
$(".spanright").click(function(){
$(".myinfo").css("color","red");
});
});
Check fiddle --
http://jsfiddle.net/swapnesh/yHRND/