JS - set window height using current window size

Question

I have some CSS that needs the body to have a height set, but this needs to be done depending on the user.

I have made some code that kind of works - it calculates the window height but it's not changing the body height. What am I doing wrong?

function setWindowHeight(){
    var windowHeight = window.innerHeight;
    document.getElementsByTagName('body').style.height = windowHeight + "px";
}

Answer 1

You need to add an eventListener, and you don't need to use the getElementsByTagName because has only 1 body tag:

function setWindowHeight(){
    var windowHeight = window.innerHeight;
    document.body.style.height = windowHeight + "px";
    console.log(document.body.style.height);
}
window.addEventListener("resize",setWindowHeight,false);

Or, if you want to use, you can do this:

function setWindowHeight(){
    var windowHeight = window.innerHeight;
    document.getElementsByTagName('body')[0].style.height = windowHeight + "px";
    console.log(document.body.style.height);
//---------------------------------------´
//will get the first element tagged body
}
window.addEventListener("resize",setWindowHeight,false);

EDIT (Changed the code above): you can check the value in the Firefox Console. Open it(CTRL + SHIFT + K) and resize the window, you will see the event resize be fired when you do it.

Answer 2

try this may work 

document.getElementsByTagName('body').height  = windowHeight + "px";