perf fix for Duplex require replacement

ofrobots · ofrobots · commit 670ddf3a27cb · 2015-11-26T12:25:05.000-08:00
I was noticing that RegExps called from Module._resolveLookupPaths were getting
to be the hottest symbol in some profiles. readable-stream seems to be requiring
Duplex from inside functions. It would be faster to not do a require on each
invocation of Readable, ReadableState, Writable, WritableState.
diff --git a/build/files.js b/build/files.js
@@ -31,9 +31,11 @@ const headRegexp = /(^module.exports = \w+;?)/m
         , '$1\n\n/*<replacement>*/\nvar Buffer = require(\'buffer\').Buffer;\n/*</replacement>*/\n'
       ]
 
+      // The browser build ends up with a circular dependency, so the require is
+      // done lazily, but cached.
     , addDuplexRequire = [
           /^(function (?:Writable|Readable)(?:State)?.*{)/gm
-        , '$1\n  var Duplex = require(\'./_stream_duplex\');\n'
+        , 'var Duplex;\n$1\n  Duplex = Duplex || require(\'./_stream_duplex\');\n'
       ]
 
     , altForEachImplReplacement = require('./common-replacements').altForEachImplReplacement

Original file line number	Diff line number	Diff line change
`@@ -31,9 +31,11 @@ const headRegexp = /(^module.exports = \w+;?)/m`
`31`	`31`	`, '$1\n\n/<replacement>/\nvar Buffer = require(\'buffer\').Buffer;\n/</replacement>/\n'`
`32`	`32`	`]`
`33`	`33`
	`34`	`+ // The browser build ends up with a circular dependency, so the require is`
	`35`	`+ // done lazily, but cached.`
`34`	`36`	`, addDuplexRequire = [`
`35`	`37`	`/^(function (?:Writable\|Readable)(?:State)?.*{)/gm`
`36`		`- , '$1\n var Duplex = require(\'./_stream_duplex\');\n'`
	`38`	`+ , 'var Duplex;\n$1\n Duplex = Duplex \|\| require(\'./_stream_duplex\');\n'`
`37`	`39`	`]`
`38`	`40`
`39`	`41`	`, altForEachImplReplacement = require('./common-replacements').altForEachImplReplacement`