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javascriptperformanceobjectbracketsnotation

Is bracket notation slower than period notation for accessing Object properties?

A developer on my team mentioned that accessing an Object property via dot notation is faster than bracket notation. For example:

var sample = { name: 'First Name' }
var nameBracket = sample['name']
var namePeriod = sample.name

In this case, their belief was that the assignment of namePeriod would be faster than nameBracket.

Is this true? If so, why? If not, why not?

Related: How would one test this hypothesis or a similar question to determine JS function speed?

Solution

  • When you want to try to test speeds of different approaches, it seems the defacto tool is jsperf.com.

    Someone has already questioned this, and created a test for it.

    http://jsperf.com/dot-notation-vs-square-bracket-notation

    The results seem to be about the same. What causes slowdows is when the contents of the bracket are a variable - at that point the compiler can no longer say to itself "Oh, ['foo'] is the same as .foo.. continuing on!".