On Wed, May 5, 2010 at 8:27 AM, Jordan Osete <jordan.os...@yahoo.fr> wrote: > I've been wondering for some time if there couldn't be a way to index arrays > from the last element directly. Currently if you have an array lost in a > deep objects hierarchy, you have to refer to it twice, once to access the > array itself, and once again to access its length:
A temporary helps here, as is often the case with deep hierarchies. > var lastItem = > > myObject.anArray[ myObject.anArray.length - 1 ]; > > myObject.anArray[ myObject.anArray.length - 2 ] = "foo"; a = myObject.anArray; a[a.length - 1]; a[a.length - 2] = "foo"; > As it seems hard to change the core language to be able to access stuff with > negative indexes, the idea would be just to add a method to ease getting / > setting of items based on the length of the array: It would be incompatible, since a[-1] means the same thing for arrays as for objects: the property named "-1". You can do it with slice and splice, though, if you don't want to just use a temporary: > //get the last element, same as .last( 0 ) > > var lastItem = myObject.anArray.last(); myObject.anArray.slice(-1)[0] > myObject.anArray.last( 1, "foo" ); myObject.anArray.splice(-2, 1, "foo"); With destructuring assignment, the slice usage gets to be a little more natural, though it still constructs an array unless there is some analysis done of the call site. TBH, I don't think that end-based access to arrays other than to append, a la Array.prototype.push, is common enough to warrant adding to the language. You could decorate Array.prototype with your own |last| method (including the unusual get/set overload) if you wanted, and use ES5's property-descriptor facilities to keep it from affecting iteration. Mike _______________________________________________ es-discuss mailing list es-discuss@mozilla.org https://mail.mozilla.org/listinfo/es-discuss
