javascript - Which browsers support <script async="async" />?

Question

On December 1, 2009, Google announced support for asynchronous Google Analytics tracking.

The asynchronous tracking is achieved using the async directive for the <script> tag.

Which browsers support the async directive (<script async="async" />) and since which version?

Answer 1

The async support as specified by google is achieved using two parts:

• using script on your page (the script is supplied by google) to write out a <script> tag to the DOM.

• that script has async="true" attribute to signal to compatible browsers that it can continue rendering the page.

The first part works on browsers without support for <script async.. tags, allowing them to load async with a "hack" (although a pretty solid one), and also allows rendering the page without waiting for ga.js to be retrieved.

The second part only affects compatible browsers that understand the async html attribute

• FF 3.6+
• FF for Android All Versions
• IE 10+ (starting with preview 2)
• Chrome 8+
• Chrome For Android All versions
• Safari 5.0+
• iOS Safari 5.0+
• Android Browser 3.0+ (honeycomb on up)
• Opera 15.0+
• Opera Mobile 16.0+
• Opera Mini None (as of 8.0)

The "html5 proper" way to specify async is with a <script async src="...", not <script async="true". However, initially browsers did not support this syntax, nor did they support setting the script property on referenced elements. If you want this, the list changes:

• FF 4+
• IE 10+ (preview 2 and up)
• Chrome 12+
• Chrome For Android 32+
• Safari 5.1+
• No android versions