You are binding the event handler inline in HTML also you are using jQuery to bind again inside the function which is not correct.

Just remove the inline onclick,

<input type="button" id="ImageHosting" value="To Image Hosting" />

And change JS

$(document).ready ( function () {
    $("#ImageHosting").click(function () {
       alert("test");
    });
});

Incase if this button is inserted dynamically then,

$(document).ready ( function () {
    //replace document below with enclosing container but below will work too
    $(document).on('click', "#ImageHosting", function () {
       alert("test");
    });
});

Use .live/.delegate if you older version of jQuery ( < 1.7)

Try something like this:

function myfunction() {

  var value = document.getElementById("textfield").value;
    document.getElementById('messageID').value=value;
  alert(value);

}  

<input type="button" value="Alert" onclick="myfunction()" type="button" class="btn btn-danger" id="button"/>
<textarea id="textfield">Hello World</textarea>

<input id="messageID">

The alert() function is synchronous and you can't verify what was clicked (it does not return anything), so the code below the call will be executed after it is closed (ok or close button). The alert is not used to gain user input. It is an alert, a message to the user. If you need to check what the user want, you should use confirm(). Note that the function name tells its purpose like alert.

Something like:

// if the ok button is clicked, result will be true (boolean)
var result = confirm( "Do you want to do this?" );

if ( result ) {
    // the user clicked ok
} else {
    // the user clicked cancel or closed the confirm dialog.
}

document.getElementsByClassName("addbutton") returns an Array(HTMLCollection to be precise). Also, you need to set the onclick to a function, you cannot use the syntax .onclick { }.

To set a listener for every button you will need to use a for loop somewhat like this

for(let i = 0; i < addbuttons.length; i++){
    addbuttons[i].onclick = function(){
        alert('Works!')
    }
}

Or if you are using ES6

for(let addButton of addbuttons){
    addButton.onclick = function(){
        alert('Works!')
    }
}

Probably relevant links,

https://www.w3schools.com/js/js_loop_for.asp

https://www.w3schools.com/jsref/event_onclick.asp

JavaScript is single-threaded, which means when you call a function, it blocks until it returns. When you call alert(), that passes control to the browser which decides how to handle it. It is not Javascript which is popping the UI dialog, it is the browser. alert() does not return until the browser receives the "OK" event and returns control. The javascript thread is halted until that happens.

So for at least two different reasons stated in the above paragraph, the answer is no :)

Alternatively, you can opt to not load an entire Javascript library for something as simple as this:

document.querySelector('#button').addEventListener('onclick', exit_alert);