The parsing of JavaScript can be deferred in several ways. To begin with, you can add two attributes to your scripts: Async and Defer. JavaScript can be downloaded using both attributes without pausing HTML parsing for visitors. Async actually does not pause HTML parsing for fetching the script (contrary to default behavior) but instead pauses the HTML parser to execute it after fetching it. When defer is enabled, visitors' browsers will download scripts while parsing HTML, but they will await the completion of HTML parsing before parsing the script.