http://bclary.com/2004/11/07/ecma-262.html#a-11.1.4 11.1.4 Array Initialiser | Array elements may be elided at the beginning, middle or end of the | element list. Whenever a comma in the element list is not preceded | by an AssignmentExpression (i. e., a comma at the beginning or after | another comma), the missing array element contributes to the length | of the Array and increases the index of subsequent elements. | Elided array elements are not defined. $ cat array-initialiser-hole.txt var exp = false, act = [,].hasOwnProperty("0"); print("expect: " + exp); print("actual: " + act); $ dbg.obj/js array-initialiser-hole.txt expect: false actual: true

*** This bug has been marked as a duplicate of 260106 ***