javascript, button, click

Give this a try

document.getElementsByClassName('red')[0].click();

Why [0] ? because getElementsByClassName returns classes (matching DOM elements) in form of an array, so [0] is the index here :-) And for your second button you can trigger the click using

document.querySelector("button[type=submit]").click();

By the way if you are using jquery then why don't you use

$(".red").click();
$("button[type=submit]").click();

Anyways both solutions should work. Hope that helps :-)

Use jQuery..

$('td[class="red"], button[class="btn btn-default btn-success"]').click();

It is possible to trigger a click using document.getElementsByClassName but you have to understand what you get back from document.getElementsByClassName is not an individual element, but a list which you can iterate over.

You can trigger a click for every item in a collection by doing the following:

var redClassElements = document.getElementsByClassName('red');

for(var i=0;i<redClassElements.length;i++) {
    redClassElements[i].click();
}

This will do nothing if you haven't assigned a click handler to the element click() is being called on though.

Also, do you really want to trigger a click on multiple elements? Your best bet is to assign the element an id as has been suggested to you. You can then use document.getElementById('theId').click().