Why does ",,," == Array(4) in Javascript? -

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boot interpreter/console , try comparison

> ",,," == array(4) true

why? @ first thought maybe since think of ",,," array of 4 characters '\0' terminating slice, might why, but

> "..." == array(4)

returns "false". so... why? know it's idiosyncratic bit of duck typing in javascript, curious underlines behavior. gleaned zed shaw's excellent presentation here btw.

because right hand operand converted string , string representation of array(4) ,,,:

> array(4).tostring()   ",,,"

if use array constructor function , pass number, sets length of array number. can have 4 empty indexes (same [,,,]) , default string representation of arrays comma-separated list of elements:

> ['a','b','c'].tostring()   "a,b,c"

how comparison works described in section 11.9.3 of specification. there see (x == y):

8. if type(x) either string or number , type(y) object,
return result of comparison x == toprimitive(y).

(arrays objects in javascript)

and if follow toprimitive method find it calls tostring.


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