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HTML

              
                <div id="mocha"></div>

              
            
!

CSS

              
                
              
            
!

JS

              
                // MOCHA - test

// UI
mocha.setup('bdd')

// CHAI
var assert = chai.assert;
var expect = chai.expect;
var should = chai.should();

const _compose = (...funcs) => {
    if (!funcs.length) return (...args) => args[0]
    if (funcs.length === 1) return (...args) => funcs[0](...args)
    return (...args) => {
        let tempArgs = args
        return funcs.reverse().map(fn => {
            tempArgs = [fn(...tempArgs)]
            return tempArgs
        }).pop()[0]
    }
}

const __compose = (...funcs) => {
    if (!funcs.length) return (...args) => args[0]
    if (funcs.length === 1) return (...args) => funcs[0](...args)
    return (...args) => {
        return funcs.reduceRight((a, b, i) => (i === funcs.length - 2) ? b(a(...args)) : b(a))
    }
}

const compose = (...funcs) => {
    if (!funcs.length) return (...args) => args[0]
    if (funcs.length === 1) return (...args) => funcs[0](...args)
    return funcs.reduce((a, b) => {
        return function(...args) {
            let temp1 = b(...args)
            let temp2 = a(temp1)
            return temp2
        }
    })
}

const add5 = augend => augend + 5
const mult2 = multiplier => multiplier * 2
const sum = (...summands) => summands.reduce((a, c) => a + c)
const pow = (base, exponent) => base**exponent

describe('composing functions', () => {
    it('return the same value as 3 funcs', () => {
        const data = [1, 2, 3, 4, 5] 
        expect(compose(add5, mult2, sum)(...data))
            .to.equal(add5(mult2(sum(...data))))
    })
    it('return the same value as 1 fn', () => {
        const data = [1, 2, 3, 4, 5] 
        expect(compose(sum)(data)).to.equal(sum(data))
        expect(compose(pow)(2,4)).to.equal(pow(2,4))
    })
    it('return 1st argument given 0 fns', () => {
        expect(compose()('whatever', 1)).to.equal('whatever')
    })
})

// RUN MOCHA
mocha.run()
              
            
!
999px

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