JavaScript functional programing with compose function and Array.reduce

Question

I am new to JavaScript Functional programming. In code below, compose can't work without setInterval outside it and clear as the first argument also does't give the compose initial value.

So my question is how can compose work without the setInterval?

const clear = () => console.clear()
const f1 = () => 2
const log = message => console.log(message)

const compose = (...fns) =>
    arg =>
        fns.reduce(
            (composed, f) => f(composed),
            arg
        )

setInterval(
    compose(clear, f1, log), 1000
)

FYI, compose has nothing to do with this. Please refer to the tag wiki in the future for usage. — Patrick Roberts
– Patrick Roberts, Commented Dec 13, 2017 at 8:02

klugjo · Accepted Answer · 2017-12-13 07:55:16Z

3

compose(...fns) returns a function. When used with setInterval, it is being called implicitly by the JavaScript engine.

If you want to use it directly, you can do something like:

const clear = () => console.clear()
const f1 = () => 2
const log = message => console.log(message)

const compose = (...fns) =>
    arg =>
        fns.reduce(
            (composed, f) => f(composed),
            arg
        )

compose(clear, f1, log)();

answered Dec 13, 2017 at 7:55

klugjo

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