User:Hakerh400/JavaScript Quiz

In this article I post some JavaScript snippets whose behavior may be hard to predict. If you think you know JavaScript, try to guess what each of these snippets outputs before running it.

001

0..constructor.prototype[Symbol.iterator] = a=>({next:b=>({done:1})});
let Array = [1, 2, ... 10];
let n = ~new Array.length.constructor(Array.length);
console.log(n);

002

function *a(){
  console.log('entry');
  return(yield yield)(yield yield);
}
const b = a().next.bind(a());
const c = () => ~setTimeout(() => console.log(typeof b(c).value));
for(let i = 0; i !== 5; i++) c();

003

console.log([
  a = a => b => a + b,
  b = a.call,
  c = b.bind(b),
].reduce(c));

004

console.log([
  a = (a=>(b=>b(b))(b=>c=>c?(a+=c,b(b)):a))(0),
  b = a.call,
  c = b.bind(b),
  ...a+a(),
].reduce(c)(0));

005

(([u0061])=>\u0061)({*[Symbol.iterator](){[a=5]=[,a=7]}})

006

((a,b)=>a(a(b)).length)(eval,(a=>a+((a,b)=>a(a,b))((a,[b,...c],d=[])=>b?a(a,c)+b:d,a))(`"'n\\`))

007

((a,b)=>b^=~a(a,b))((a,[b,...c],d=c[1])=>d?a(a,c):b,[a=>a,a=>b=>a,a=>(b=[a1=>a2])=>a1(a2)].reduce(function*(a,b){return a+b}).next().value)