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some esoteric ES6 functions

var getDiagonalMatrix = N=>Array(N).fill(0).map((x,i)=>Array(N).fill(i).map((x,j)=>i==j?1:0));
var getNDArray = (N, x)=>N.length?(Array(N[0]).fill(0).map(()=>arr(N.slice(1),x))):x;


var toBase =  (x,n,r=[])=>x ? toBase(Math.trunc(x/n), n, [ x%n, ...r]):r;


...........

check performance of any language/algo/something else

begin = getTime()
data = initData()

for i = 0..(2**30)
    data = doTheWork(data); // optional, looping itself takes some time too
    if(!(i & (i-1) )) // i is power of 2
        dump(i, data, getTime() - begin)






[i,x, pi, parts] = [1,1, Math.PI, []];
while(i<100){
  let n = Math.floor(x / pi**(-i));
  x -= n / pi**i;
  if(n > 3) break;
  if(n) parts.push(`${n}\\cdot\\pi^{-${i}}`);
  i++;
}
console.log(`1=${parts.join('+')}`)