function to check selected button

[rambo1]

how to write this in proper javascript way;

function check_selected_button(){
if buttonA.clicked
open in a new window
else doNothing
}

<% submit_tag "ButtonA" %>

[AlexanderZ]

Add an onclick="" handler to the <submit> button with "window.open(url, name, params) return false;" call, or add an onsubmit handler to the <form> with the same code.

[paul_wilkins]

Please do not add event attributes to HTML. They may temporarily solve the issue but just like adding style attributes to your HTML, they wind up causing more pain in the long run.

Instead, use more traditional event registration techniques.

If you have a function that you wish to attach to an event, use the following

function doSomething() {
    // ...
}
var myForm = document.getElementsById('myForm');
myForm.onclick = doSomething;

If you have lines of code that you wish to attach to an event, use an anonymous function instead.

var myForm = document.getElementsById('myForm');
myForm.onclick = function () {
    // ...
}

To place this in terms of the proposed answer, here is how it should be achieved.

var myForm = document.getElementsById('myForm');
myForm.onsubmit = function () {
    window.open('page.html', 'pageName', params);
    return false;
}