How to write a function in javascript which returns true or false as alternating when its invoked without keeping global variables using closure?

Question

the function should be like function trueOrFalse(), it should not keep anything in global scope, everything has to be scoped local to the function. the returned value should be true or false and next time it should return the inverse.

What have you tried so far? A closure, as mentioned in the title, sounds like a good start. — ASDFGerte, Oct 25 '19 at 13:20
functions are just objects - does that help - don't need *any* variables at all — Bravo, Oct 25 '19 at 13:38
Possible duplicate of [How do JavaScript closures work?](https://stackoverflow.com/questions/111102/how-do-javascript-closures-work) — Dexygen, Oct 25 '19 at 14:08
@GeorgeJempty I wouldn't say that this is a duplicate, but rather a too broad question... — FZs, Oct 25 '19 at 14:31
@GeorgeJempty , its not about `Closures`, but about implementing a particular logic using closures, its not a duplicate ! — Sandeep Vattapparambil, Oct 25 '19 at 14:34

Moritz Roessler · Accepted Answer · 2019-10-25T13:50:24.127

2

You're on the right track. A closure and a local variable is all you need.

function gen () {
    let state = false;
    return function () {
        return state = !state;
    }
}
const trueFalse = gen();

trueFalse() //true
trueFalse() //false

Regarding the comment, it's possible to do this without a closure using a property on the function itself.

function trueOrFalse () {
    return trueOrFalse.state = !trueOrFalse.state;
}
trueOrFalse() //true
trueOrFalse() //false

edited Oct 25 '19 at 13:50

answered Oct 25 '19 at 13:36

Moritz Roessler

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yes, but can you write it exactly as asked: `function trueOrFalse() {...}` and no other code? – georg Oct 25 '19 at 13:46
@georg Yes, you could use a property on the function itself – Moritz Roessler Oct 25 '19 at 13:49

How to write a function in javascript which returns true or false as alternating when its invoked without keeping global variables using closure?

1 Answers1