#9025, #9750 - jQuery.map - bounding values and Functions as no arrays. #368
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…he line for more clarity.
| @@ -720,7 +720,9 @@ jQuery.extend({ | |||
| i = 0, | |||
| length = elems.length, | |||
| // jquery objects are treated as arrays | |||
| isArray = elems instanceof jQuery || length !== undefined && typeof length === "number" && ( ( length > 0 && elems[ 0 ] && elems[ length -1 ] ) || length === 0 || jQuery.isArray( elems ) ) ; | |||
| isArray = elems instanceof jQuery || length !== undefined && typeof length === "number" && ( | |||
| length > 0 && ( ( 0 in elems ) && ( length - 1 in elems ) || jQuery.isArray( elems ) ) || | |||
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What's the benefit to doing ( 0 in elems ) over elems [ 0 ]
I was originally thinking performance.. but i guess it varies.. http://jsperf.com/in-vs-arr-key
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Take for example an arguments object which first (or last) value is 0. Currently such object will be traversed as an object, and not as an array! Using the in operator instead, only the presence of the first and last property is checked, and not their values too.
EDIT: Also, seams that using in is generally considerably faster, with the exception of Chrome...
Note that arguments object is not an ideal example here, because their properties as length and callee are generally not enumerable, so it is less important in which way it is traversed. However, other array-like objects can not be ignored (see test of #9025).
EDIT: Seams arguments is still a good example because of #9750.
Ensure all values are considered in .map
Bug #9025 to reopen->close (false duplicate).
Ensure that functions with length == 0 (with no arguments) are not traversed as arrays.
ALSO: Ensure that .isArray() is not unnecessarily called when length == 0.