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Jan Küster
Jan Küster

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JavaScript code puzzle: convert a Boolean to Number

Write a function fn that receives a Boolean and returns it's representation as a Number. So true becomes 1 and false becomes 0.


  • no Number constructor or any of it's prototype allowed
  • no Math functions allowed
  • no toNumber implementations allowed either
  • Strings of numbers, such as '1' and '0' do not count
  • Assume the function always receives a valid boolean (so no null or undefined or other types need to be considered).


 console.assert(fn(true) === 1)
 console.assert(fn(false) === 0)
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It's marked as #beginners, because it's solution easier than you might think.


It's possible to solve it with 9 characters overall.

Top comments (2)

snigo profile image
Igor Snitkin

Up to 3 characters:

const fn_not = b => ~~b;
const fn_inc = b => b++;
const fn_nry = b => +b; // might fall under `toNumber` implementation
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Cool stuff, keep it up!

jankapunkt profile image
Jan Küster

Another solution with same length would be

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I counted the function too, which I came up to 9 characters