521391 - [HTML5] Provide a dev doc explaining how to avoid speculation failures

Status: RESOLVED FIXED

(Developer Documentation Graveyard :: HTML, defect, P3)

Description

[Henri Sivonen (:hsivonen)]

Bug 482919 will introduce speculative parsing to the HTML5 parser. Web authors who care about the load times of their pages should avoid the kind of document.write() use that makes speculations fail.

Need to provide a DevMo article that explains what the pitfalls are.

 * Don't put "\r" at the end of your last document.write() in a script. (Hopefully people who document.write() line breaks use "\n" anyway.)

 * Don't write unbalanced trees. <script>document.write("<div>");</script> is bad.

 * Don't document.write() and unfinished token. <script>document.write("<div ");</script> is bad.

 * Need to explain the situation where formatting elements interfere. That is the cases where <b><script>document.write("...");</script></b> is bad.

 * Don't insert from script or document.write() a <base> element. (Doesn't cause speculative parse to fail but causes speculative loads to fail.)

Comment 1

[Henri Sivonen (:hsivonen)]

Draft: https://developer.mozilla.org/en/Optimizing_Your_Pages_for_Speculative_Parsing

Comment 2

[Skip Geel]

The page says <script>document.write("<div></div>");</script> is good. ALMOST.
<script>document.write("<div><\/div>");</script> is good.
Remember, the parser stops scanning when it reaches the first "</".

Comment 3

[Henri Sivonen (:hsivonen)]

(In reply to comment #2)
> The page says <script>document.write("<div></div>");</script> is good.
> ALMOST.
> <script>document.write("<div><\/div>");</script> is good.
> Remember, the parser stops scanning when it reaches the first "</".

Not so. See http://www.whatwg.org/specs/web-apps/current-work/multipage/tokenization.html#script-data-end-tag-open-state and the related states.

Comment 4

[Henri Sivonen (:hsivonen)]

FIXED per comment 1.