wuct/promise-fmap.js

Last active November 3, 2018 20:18

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Let JavaScript Promise be a functor

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promise-fmap.js

	Promise.prototype.fmap = Promise.prototype.then

	Promise.resolve('yolo')
	.fmap(str => str + ' swag!')
	.then(console.log) // "yolo swag!"

modern-defensive commented Nov 3, 2018

promise.then(x => g(f(x))) is NOT equivalent to promise.then(f).then(g)
see
https://stackoverflow.com/questions/45712106/why-are-promises-monads

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