are external javascript files loaded sequentially or parallel?
if i have multiple script tags in my page like:
-
Short: Yes:
Without specifying
deferorasyncproperties within the script tag, the spec says, that a browser has to sequentially (sync) load those files.In other words, a plain script tag which a browser finds needs to get
- loaded
- executed
- (block any other render/execution process while doing the above)
While a "modern" browser probably still trys to optimize that process, those steps need to be applied (at least, process-like). That is the reason why you should place script tags without further specification always at the bottom of your
<body>tag. Even the DOM render process stops while loading/executing scripts.To avoid that, you can specify a
deferorasync(HTML5 only) property in those script tags, like<script defer src="/foo/bar.js"></script>that tells the browser it is a script that meant to be executed after the document has been parsed.
See https://developer.mozilla.org/En/HTML/Element/Script
讨论(0) -
They are loaded in parallel but they run only once every file have been loaded. So the answer is yes, you can rely on the fact.
讨论(0) -
In general, scripts are downloaded sequentially (see this page):
Because JavaScript code can alter the content and layout of a web page, the browser delays rendering any content that follows a script tag until that script has been downloaded, parsed and executed. However, more importantly for round-trip times, many browsers block the downloading of resources [such as stylesheets, images, and other scripts] referenced in the document after scripts until those scripts are downloaded and executed.
讨论(0) -
They may be loaded (via the network) in parallel, but they are evaluated in sequence.
So yes, you can rely on the order.
讨论(0)
加载中...
- 热议问题