Why is document.body null? Javascript

Question

I created the following code:
function btn(text, does)
{
var button = document.createElement("button");
button.innerHTML = text;

button.addEventListener("click" , does );

document.body.appendChild(button);
}//ends function btn

function say() {
document.write("text");

}

btn("Click me", say );

This code results in a error: "Cannot read property 'appendChild' of null"
From my googling I learned that the issues is that document.body is null (appendChild is a property of document.body but d.b is null so it cannot read it). Why is my document.body null?

I think other people have been able to run this code just fine, yet it does not work for me. I have tried it on IE, Edge and Chrome. Thanks

Link to this code: https://code.sololearn.com/W7QAzI0bkJs3/#js (I hope it works)

Answer 1

I believe your function is being called before the body is created. To solve this, wrap the function inside an onload event to ensure everything has been loaded in

window.onload = function(){
btn("click me", say)
}

Answer 2

THANK YOU! It works now