Edward Lee wrote: > Right now [].reduce doesn't take an optional thisArg, so the callback > is always called with |null| for |this| per 9.c.ii. > > The Array prototype object take an optional thisArg for every, some, > forEach, map, and filter; so it would be good to make reduce > consistent with the rest.
Why is it better to use 'this' than to simply have the callback function capture the variables it needs? The latter is just as expressive and IMHO results in clearer code, since: - the captured variables are named, and the names can be more meaningful than 'this'; - there can be more than one such variable, without needing to set 'this' to an object or list. The required variables are necessarily in scope when passing a FunctionExpression as the callback. The case where they are not in scope because the callback function is defined elsewhere is quite unusual; in that case, you can instead pass a lambda expression that calls the function defined elsewhere with these variables as explicit parameters. (That is a situation where using 'this' results in particularly *unclear* code, because the definition of what 'this' is set to may be far away from its use.) The other methods with callbacks take a 'thisArg' not because it is needed or even useful, but for compatibility, because they already do in existing implementations that provide these functions. -- David-Sarah Hopwood ⚥ _______________________________________________ Es-discuss mailing list [email protected] https://mail.mozilla.org/listinfo/es-discuss
