386030 - Array.reduce should ignore holes

Status: VERIFIED FIXED

(Core :: JavaScript Engine, defect)

Description

[nanto_vi (TOYAMA Nao)]

Array extra methods that are introduced in JS 1.6 ignore hole elements.  But reduce/reduceRight don't if the initial value isn't given and the hole element is the first element (reduce) or the last element (reduceRight).  To keep consitency, reduce/reduceRight should start iteration from the first non-hole element or throw "reduce of empty array with no initial value" error if no such element exists.

Actual:
js> function add(a, b) { return a + b; }
js> // Non-first hole elements are ignored.
js> a = new Array(2); a[0] = 3; a.reduce(add);
3
js> // If initial is given, the first hole is ignored.
js> a = new Array(2); a[1] = 3; a.reduce(add, 0);
3
js> a = new Array(2); a[1] = 3; a.reduce(add);
NaN
js> a = new Array(2); a[0] = 3; a.reduceRight(add);
NaN
js> uneval(new Array(2).reduce(add))
(void 0)

Expected:
js> a = new Array(2); a[1] = 3; a.reduce(add);
3
js> a = new Array(2); a[0] = 3; a.reduceRight(add);
3
js> uneval(new Array(2).reduce(add))
TypeError: reduce of empty array with no initial value

Comment 1

[Blake Kaplan (:mrbkap) (inactive)]

Attachment: Proposed fix

Comment 2

[Blake Kaplan (:mrbkap) (inactive)]

Attachment: Small shell-based testcases

This is the interesting subset of testcases, I think.

Comment 3

[Blake Kaplan (:mrbkap) (inactive)]

Fix checked into trunk.

Comment 4

[Jeff Walden [:Waldo]]

I updated the MDC implementations for this.

http://developer.mozilla.org/en/docs/Core_JavaScript_1.5_Reference:Objects:Array:reduce
http://developer.mozilla.org/en/docs/Core_JavaScript_1.5_Reference:Objects:Array:reduceRight

Comment 5

[Bob Clary [:bc] (inactive)]

/cvsroot/mozilla/js/tests/js1_6/Array/regress-386030.js,v  <--  regress-386030.js
initial revision: 1.1

Comment 6

[Bob Clary [:bc] (inactive)]

this should have been in js1_7. I'll move it when I add reduce* object detection to skip the reduce tests on the 1.8 branch.

Comment 7

[Bob Clary [:bc] (inactive)]

verified fixed 1.9.0 linux/mac*/windows