I have been reading over the `.forEach` with a return value discussion. I imagine if that was added it would work with chaining and do everything that `.tap` would be capable of. Unless I have missed something?
On Jul 16, 2017 3:55 PM, "Eli White" <[email protected]> wrote: > This is definitely something that can be polyfilled (with different levels > of naivety) but requires modifying built-ins which is a no-no. > > Here is an example that is more valuable in production than just debugging. > > Many other languages that support `.tap` enable a value to be returned. If > it is, that value is passed down the rest of the chain instead of the > initial value (but the return value is optional). This is also functionally > similar to `.tee` in many languages (and bash). > https://en.wikipedia.org/wiki/Tee_(command) > > One of the other common use cases for `.tap` is to be able to chain > methods that act on the entire array. For example, if `.reverse` wasn't > part of `Array.prototype` and instead you had a user function > `myReverse(arr) => arr'`, then if you wanted to convert `[1,2,3]` into > `["6","4","2"]`, then you'd have to do the following. It is a bit of a > contrived example since I'm avoiding just calling `myReverse` before or > after the chain. Imagine a more complex example and longer chain. > > ``` > const value = [1, 2, 3].map(String); > myReverse(value).map(num => num * 2); > ``` > > With `.tap`, it can be part of the chain: > > ``` > const value = [1, 2, 3] > .map(String) > .tap(myReverse) > .map(num => num * 2); > ``` > > Obviously this could be done with reduce, but it would require `myReverse` > to have a different signature. > > Just trying to provide some reasoning why `.tap` is for more than just > debugging. :) > > > On Sun, Jul 16, 2017 at 12:00 PM, Bob Myers <[email protected]> wrote: > >> ```js >> Object.defineProperty(Array.prototype, 'tap', { >> value: function(fn) { fn(this); return this;} >> }); >> ``` >> >> On Mon, Jul 17, 2017 at 12:15 AM, Logan Smyth <[email protected]> >> wrote: >> >>> You could always hack it and use the third argument :D >>> >>> ``` >>> var tap = f => (v, i, arr) => { >>> if (i === arr.length - 1) f(arr); >>> >>> return v; >>> }; >>> ``` >>> >>> Fine for debugging at least, but not necessarily your overall goal. >>> >>> On Sun, Jul 16, 2017 at 11:20 AM, Eli White <[email protected]> wrote: >>> >>>> That leads to a different result. Map is called once for every item in >>>> the array. >>>> >>>> ``` >>>> const tap = f => x => { >>>> f(x); >>>> return x; >>>> } >>>> >>>> [1, 2, 3] >>>> .map(num => num * 2) >>>> .map(tap(console.log.bind(console))) >>>> .reduce((a, b) => a + b); >>>> ``` >>>> >>>> Results in: >>>> >>>> ``` >>>> 2 >>>> 4 >>>> 6 >>>> ``` >>>> >>>> Whereas >>>> >>>> ``` >>>> [1, 2, 3] >>>> .map(num => num * 2) >>>> .tap(console.log.bind(console)); >>>> .reduce((a, b) => a + b); >>>> ``` >>>> >>>> would result in >>>> >>>> ``` >>>> [2, 4, 6] >>>> ``` >>>> >>>> This is what makes it hard about being a userland function. Tap enables >>>> the developer to act on the *entire* array, not individual items. >>>> >>>> On Sun, Jul 16, 2017 at 11:10 AM, Elie Rotenberg <[email protected]> >>>> wrote: >>>> >>>>> Sorry I meant: >>>>> >>>>> const tap = f => x => { >>>>> f(x); >>>>> return x; >>>>> } >>>>> >>>>> >>>>> Elie ROTENBERG >>>>> Directeur général adjoint >>>>> [email protected] >>>>> 336 89 29 98 19 >>>>> twitter elierotenberg facebook elie.rotenberg skype elie.rotenberg >>>>> github elierotenberg >>>>> 2, rue Paul Vaillant Couturier - CS 60102 - 92532 Levallois-Perret >>>>> Cedex - T: 33 811 69 41 42 >>>>> >>>>> >>>>> On Sun, Jul 16, 2017 at 8:09 PM, Elie Rotenberg <[email protected]> >>>>> wrote: >>>>> >>>>>> I think the most common use of this pattern would be debugging, and >>>>>> in this context you don't really care to use a little helper and >>>>>> Array.prototype.map, eg: >>>>>> >>>>>> const tap = f => ...args => { >>>>>> f(...args); >>>>>> return x; >>>>>> }; >>>>>> >>>>>> [1, 2, 3] >>>>>> .map(num => num * 2) >>>>>> .map(tap(console.log.bind(console))); >>>>>> .reduce((a, b) => a + b); >>>>>> >>>>>> >>>>>> On Sun, Jul 16, 2017 at 8:00 PM, Eli White <[email protected]> >>>>>> wrote: >>>>>> >>>>>>> I'd like to propose a `.tap` method on the Array prototype. I was >>>>>>> able to find some previous discussion here but it was off the main topic >>>>>>> and seemed to die out: https://mail.mozilla.org/ >>>>>>> pipermail/es-discuss/2015-October/044454.html >>>>>>> >>>>>>> A tap method enables the user to inspect an array in the chain. >>>>>>> >>>>>>> For example, inspection: >>>>>>> >>>>>>> If you have a chain like this: >>>>>>> >>>>>>> ``` >>>>>>> [1, 2, 3] >>>>>>> .map(num => num * 2) >>>>>>> .reduce((a, b) => a + b); >>>>>>> ``` >>>>>>> >>>>>>> When you want to see what the value of the array is between the map >>>>>>> and reduce, you would typically do this: >>>>>>> >>>>>>> ``` >>>>>>> const value = [1, 2, 3] >>>>>>> .map(num => num * 2); >>>>>>> >>>>>>> console.log(value); >>>>>>> >>>>>>> value.reduce((a, b) => a + b); >>>>>>> ``` >>>>>>> >>>>>>> With `.tap`, you'd be able to do this: >>>>>>> >>>>>>> ``` >>>>>>> [1, 2, 3] >>>>>>> .map(num => num * 2) >>>>>>> .tap(console.log.bind(console)); >>>>>>> .reduce((a, b) => a + b); >>>>>>> ``` >>>>>>> >>>>>>> `.tap` would be called once, passed the entire array as the first >>>>>>> argument to the callback, and would return the array after the callback >>>>>>> was >>>>>>> finished. >>>>>>> >>>>>>> This isn't something that can cleanly be done with a user-land >>>>>>> function since it would have to wrap the chain, or replace all of the >>>>>>> chained functions like underscore does. >>>>>>> >>>>>>> An example of wrapping the chain: >>>>>>> >>>>>>> ``` >>>>>>> myTap( >>>>>>> ( >>>>>>> [1, 2, 3] >>>>>>> .map(num => num * 2) >>>>>>> ), >>>>>>> console.log.bind(console); >>>>>>> ) >>>>>>> .reduce((a, b) => a + b); >>>>>>> ``` >>>>>>> >>>>>>> _______________________________________________ >>>>>>> es-discuss mailing list >>>>>>> [email protected] >>>>>>> https://mail.mozilla.org/listinfo/es-discuss >>>>>>> >>>>>>> >>>>>> >>>>> >>>> >>>> _______________________________________________ >>>> es-discuss mailing list >>>> [email protected] >>>> https://mail.mozilla.org/listinfo/es-discuss >>>> >>>> >>> >>> _______________________________________________ >>> es-discuss mailing list >>> [email protected] >>> https://mail.mozilla.org/listinfo/es-discuss >>> >>> >> > > _______________________________________________ > es-discuss mailing list > [email protected] > https://mail.mozilla.org/listinfo/es-discuss > >
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