javascript - switch-case performance in ECMAscript -

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i'm using switch-case statements on regular bases in ecmascript. beside personal endorsement it, there tons of specialist literature out, performance in language in general , conditional statements specifically.

one example remember instance, excellent book "high performance javascript" nicholas zakas. in many other books , articles, said switch-case statement faster if (else) statements, when you're using more two conditional cases.

in c-like language know of, switch-case statement nothing else binary-hash-map which, broken down again, chain of jmp codes in assembly. have read here

however, after foreword:

i had discussion usage of event handler functions team , how going deal event types. whether or not going use explicit function event, or if should use 1 big function handles multiple event types. within discussion, performance question developed , created basic, simple jsperf:

http://jsperf.com/engine-context-data-caching-test/3

and pretty shocked results , saw. believing in these test-cases, order of case statements drastically important on performance of execution. difference between long , longslow there, position of case 'baz' statement within switch statement. real , reasonable?

is there chance overlook ? first, thought well, maybe not enough case statements , interpreter create if-else conditions under hood, increased number without change in results.

i refuse believe ecmascript engines v8 , spidermonkey, still don't optimize issue.

i'm referencing source: http://oreilly.com/server-administration/excerpts/even-faster-websites/writing-efficient-javascript.html#sect2

use if statement when:

  • there no more 2 discrete values test.

  • there large number of values can separated ranges.

use switch statement when:

  • there more 2 fewer 10 discrete values test.

  • there no ranges conditions because values nonlinear.

use array lookup when:

  • there more 10 values test.

  • the results of conditions single values rather number of actions taken.


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