Get div height with plain JavaScript

var clientHeight = document.getElementById('myDiv').clientHeight;

or

var offsetHeight = document.getElementById('myDiv').offsetHeight;

clientHeight includes padding.

offsetHeight includes padding, scrollBar and borders.

jsFiddle

var element = document.getElementById('element');
alert(element.offsetHeight);

Another option is to use the getBoundingClientRect function. Please note that getBoundingClientRect will return an empty rect if the element's display is 'none'.

Example:

var elem = document.getElementById("myDiv");
if(elem) {
  var rect = elem.getBoundingClientRect();
  console.log("height: " + rect.height);  
}

UPDATE: Here is the same code written in 2020:

const elem = document.querySelector("#myDiv");
if(elem) {
  const rect = elem.getBoundingClientRect();
  console.log(`height: ${rect.height}`);
}