HTML DOM Script async attribute

Examples

Check whether the script is executed asynchronously (Once a script is available):

var x = document.getElementById("myScript").async

x The output is:

true

async property sets or returns whether asynchronous execution script (script once available).

This property reflects the async attribute <script> tag.

Note: async property applies only to external script (only when using the src attribute).

Note: There are several ways to perform an external script:

If async = "async": script asynchronously with respect to the rest of the page execution (when the page continues to be parsed, the script will be executed)
When the script execution will be completed parsing the page: If you do not use the async and defer = "defer"
If neither use nor async defer: Before the browser to continue parsing the page, immediately read and execute scripts

All major browsers support async attribute.

Note: IE 9 and previous versions of Opera version 12 and earlier do not support async attribute.

Returns async attribute:

scriptObject .async

Set the async property:

scriptObject .async=true|false

值	描述
true\|false	规定是否异步执行脚本（一旦脚本可用）。 true - 异步执行脚本（一旦脚本可用）。The script will be executed asynchronously as soon as it is available false - 脚本不会异步执行（一旦脚本可用）。

return value:	Boolean value that, if the asynchronous execution of the script (script once available), it returns true, otherwise returns false.