async attribute | async property
Provides control of when a script executes while a document loads. Setting a script to run asynchronously can improve performance by unblocking the rest of the document. When async = false, it can preserve execution order to ensure dependent scripts are run in order.
This property is read/write.
<element async="ptr" ... >
object.async = ptr ptr = object.async
When true, the script will execute asynchronously, otherwise script is executed as page loads.