demonstrating a use case for condition variables in JavaScript

CondVar.js

const asyncMeaningOfLife = () =>
    Promise.resolve({ meaningOfLife: 42 })

const updateResult = result => update =>
    Object.assign(result, update, { processing: false })

function syncFun(afterUpdate) {
    const result = { processing: true }

    asyncMeaningOfLife()
    .then(updateResult(result))
    .then(afterUpdate)

    return result
}

function CondVar() {
    let signal
    const waitPromise = new Promise(resolve => { signal = resolve })
    return { signal
           , wait: () => waitPromise
           }
}

describe(`syncFun`, () => {
    it('should eventually produce the meaning of life', async () => {
        const condVar = CondVar()
        const result = syncFun(condVar.signal)
        expect(result.processing).toBe(true)

        await condVar.wait()
        expect(result.processing).toBe(false)
        expect(result.meaningOfLife).toBe(42)
    })
})