Won't work for an explicitly pass undefined because that triggers assignment of the default value
Axel Rauschmayer <[email protected]> wrote: >How about the following solution? > > > let missingArgument = {}; // or a symbol > > function reduce(callback, initial = missingArgument){ > > let startIndex; > > > > if (initial === missingArgument) { > > initial = this[0]; > > startIndex = 1; > > } else { > > startIndex = 0; > > } > > > > ...etc... > > } > > >On Dec 24, 2012, at 3:32 , Allen Wirfs-Brock <[email protected]> wrote: > > >On Dec 23, 2012, at 5:35 PM, Brandon Benvie wrote: > >Here's one of the examples that was sticking out in my mind earlier that >Brendan's solution takes care of. Array.prototype.reduce requires that if the >initial value isn't provided then the first value of the array is the initial >value. > >Using rest: > > function reduce(callback, ...initial){ > var current, index; > > if (initial.length) { > index = 0; > current = initial[0]; > } else { > index = 1; > current = this[0]; > } > > ...etc... > } > > >the way I would express this example is: > >function reduce(callback, ...rest){ > var current, index; > if (rest.length > 0) { > index = 0; > current = rest[0]; > } else { > index = 1; > current = this[0]; > } > ...etc... >} > >which seems to exactly express the intent > > >-- > >Dr. Axel Rauschmayer > >[email protected] > > >home: rauschma.de > >twitter: twitter.com/rauschma > >blog: 2ality.com > >
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