"Cannot read property 'addEventListener' of null"

Question

my code is presenting to me this error in the title
the code :

//gets the element vel by its id and sets it to a variable
var vel = document.getElementById("vel");
vel.addEventListener("click", function() {
//gets these 2 elements by thier ids
var d = document.getElementById("d");
var t = document.getElementById("t");
//sets the result var
var result = d / t;
//get the <p> tag by its id and then puts the result into it.
var x = document.getElementById("res");
x.innerHTML = result
});

Answer 1

It's just bcz your JS gets loaded before the HTML part and so it can't find that element.
Just put your whole JS code inside a function which will be called when the window gets loaded.
You can do like this is your JS

window.onload= function (){
//Your entire JS code here
}

Answer 2

It means there's no element with id "vel"
Maybe check your html

Answer 3

In addition to what Flandre Scarlet said, make sure you are accessing the element after it has been created in the DOM. Something like document.onload would do the trick.

Answer 4

replying to shashi ranja:
thanks a lot

Answer 5

It is because the variable is not defined yet. You probably have not saved the html yet or have not defined it yet.