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composition can be seeded with multiple arguments #1050

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merged 4 commits into from
Dec 12, 2015
Merged

composition can be seeded with multiple arguments #1050

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8e19d06
composition can be seeded with multiple arguments
Bjvanminnen Nov 18, 2015
306094d
handle compose with no functions
Bjvanminnen Nov 19, 2015
0121689
more verbose, but easier to follow
Bjvanminnen Nov 26, 2015
422c37a
remove semicolons
Bjvanminnen Nov 27, 2015
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6 changes: 5 additions & 1 deletion src/utils/compose.js
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Original file line number Diff line number Diff line change
Expand Up @@ -6,5 +6,9 @@
* left. For example, compose(f, g, h) is identical to arg => f(g(h(arg))).
*/
export default function compose(...funcs) {
return arg => funcs.reduceRight((composed, f) => f(composed), arg)
return (...args) => {
return funcs.length ?
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It is a little hard to grasp what this is doing at first.
Maybe re-writing this as an if statement would make this function a bit easier to follow.

funcs.slice(0, -1).reduceRight((composed, f) => f(composed), funcs[funcs.length - 1](...args)) :
args[0]
}
}
12 changes: 12 additions & 0 deletions test/utils/compose.spec.js
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Expand Up @@ -21,5 +21,17 @@ describe('Utils', () => {
expect(compose(b, c, a)(final)('')).toBe('bca')
expect(compose(c, a, b)(final)('')).toBe('cab')
})

it('can be seeded with multiple arguments', () => {
const square = x => x * x
const add = (x, y) => x + y
expect(compose(square, add)(1, 2)).toBe(9)
})

it('returns the first given argument if given no functions', () => {
expect(compose()(1, 2)).toBe(1)
expect(compose()(3)).toBe(3)
expect(compose()()).toBe(undefined)
})
})
})