document get by class name code example
Example 1: javascript get element by class
var elementsArray = document.getElementsByClassName("someclassname");
Example 2: javascript get element by class
var elements = document.querySelector(".class");
Example 3: get elment by id within get element byclassname
var targetDiv = document.getElementById("foo").getElementsByClassName("bar")[0];
targetDiv.textContent = "Goodbye world!";