Is rewrite_javascript_external enabled by default?

Yes. rewrite_javascript_external is in CoreFilters, the default RewriteLevel, so it runs unless you turn it off with DisableFilters. It is also part of the OptimizeForBandwidth level.

How do I turn off rewrite_javascript_external?

Add ModPagespeedDisableFilters rewrite_javascript_external on Apache or pagespeed DisableFilters rewrite_javascript_external; on nginx. On IIS, add pagespeed DisableFilters rewrite_javascript_external to pagespeed.config.

Minify external JavaScript (rewrite_javascript_external)

Q: What does the rewrite_javascript_external filter do?

rewrite_javascript_external handles the external half. Each file on a domain the module is authorized to fetch is minified and served from a rewritten .pagespeed.jm. URL with a long cache lifetime, so repeat visitors download the minified file once and keep it; the original file on disk is never modified. In OptimizeForBandwidth mode the minified bytes replace the original response in place and the URL stays as authored.

Category:: JavaScript
CoreFilters:: Yes
OptimizeForBandwidth:: Yes
Risk:: Generally safe

rewrite_javascript_external handles the external half. Each <script src> file on a domain the module is authorized to fetch is minified and served from a rewritten .pagespeed.jm. URL with a long cache lifetime, so repeat visitors download the minified file once and keep it; the original file on disk is never modified. In OptimizeForBandwidth mode the minified bytes replace the original response in place and the URL stays as authored.

How it works

The three filters on this section share one minifier. It removes comments and collapses whitespace; identifiers, string literals, regular expressions and property names are emitted unchanged. It keeps a line break wherever automatic semicolon insertion could otherwise merge two statements into one. How safe JavaScript minification handles automatic semicolon insertion has the details.

Minification saves the most on hand-formatted source; a file a bundler already minified gains nothing and only costs rewrite time. rewrite_javascript_external runs as part of the compound and can also be enabled on its own.

Enabled on its own, rewrite_javascript_external leaves inline <script> blocks exactly as authored; minifying those is the inline sub-filter’s job. Files on domains the configuration does not authorize keep their original URLs as well, so a page that mixes own and third-party scripts sees only the own files rewritten.

When to use it

In CoreFilters, the default RewriteLevel: it runs unless you disable it.
Part of OptimizeForBandwidth, the level that optimizes resources without changing their URLs.
Also switched on by rewrite_javascript.
Risk rating on these docs: Generally safe.

Risks

The minifier never renames identifiers; the historical failure mode is a script that inspects its own source text, for example through Function.prototype.toString(), and reacts to the changed formatting.
Verify with the X-Mod-Pagespeed response header and a ?PageSpeedFilters=-rewrite_javascript comparison; Is it working? has the steps.

Configuration

Enable it in the module configuration, at server, virtual-host or location scope:

Apache

ModPagespeedEnableFilters rewrite_javascript_external

nginx

pagespeed EnableFilters rewrite_javascript_external;

IIS (pagespeed.config)

pagespeed EnableFilters rewrite_javascript_external

It is on by default under CoreFilters; to turn it off:

ModPagespeedDisableFilters rewrite_javascript_external   # Apache
pagespeed DisableFilters rewrite_javascript_external;   # nginx
pagespeed DisableFilters rewrite_javascript_external   # IIS

Scoping, ForbidFilters and the thresholds filters read: Choosing filters .

Frequently asked questions

What does the rewrite_javascript_external filter do?: rewrite_javascript_external handles the external half. Each <script src> file on a domain the module is authorized to fetch is minified and served from a rewritten .pagespeed.jm. URL with a long cache lifetime, so repeat visitors download the minified file once and keep it; the original file on disk is never modified. In OptimizeForBandwidth mode the minified bytes replace the original response in place and the URL stays as authored.
Is rewrite_javascript_external enabled by default?: Yes. rewrite_javascript_external is in CoreFilters, the default RewriteLevel, so it runs unless you turn it off with DisableFilters. It is also part of the OptimizeForBandwidth level.
How do I turn off rewrite_javascript_external?: Add ModPagespeedDisableFilters rewrite_javascript_external on Apache or pagespeed DisableFilters rewrite_javascript_external; on nginx. On IIS, add pagespeed DisableFilters rewrite_javascript_external to pagespeed.config.

rewrite_javascript — Minify JavaScript
rewrite_javascript_inline — Minify inline JavaScript
combine_javascript — Combine JavaScript
defer_javascript — Defer JavaScript
extend_cache_scripts — Extend cache for scripts
include_js_source_maps — Include JS source maps
inline_javascript — Inline JavaScript
make_show_ads_async — Async AdSense

This page is drawn from the rewrite_javascript_external entry on JavaScript filters. Every filter in one table: PageSpeed filters.