Select an element by ID
getElementById - a fast and cross browser safe way for selecting DOM elements.
getElementById() is supported in all major browsers and returns the first element with the specified ID. It is the fastest way for accessing DOM tree elements. Example:
var el = document.getElementById('foo');
el.innerHTML = 'Hello World!';
The method is blazingly fast, but due to the limitation of selecting elements only by id, its usefulness is limited. The linked reference shows a performance comparison between
querySelectorAll(). The latter is a convenient method for accessing DOM elements by almost arbitrary CSS selectors.