3reel slot calc.

calc.js

/* 3 reel slot, no wilds, no scatter*/

function occur(array){
const occurrences = array.reduce(function (acc, curr) {
  return acc[curr] ? ++acc[curr] : acc[curr] = 1, acc
}, {});	
return occurrences;
}

const reels = [
[6,2,2,2,2,4,4,8,1,1,1,1,0,7,0,0,0,0,5,5,3,3,3,3], 
[7,6,2,6,2,2,2,4,1,4,1,1,1,0,8,0,0,0,5,3,5,3,3,3], 
[0,0,0,0,5,5,8,3,3,3,3,6,6,2,2,2,2,4,4,1,1,1,1,1,0,7]
];
		
const paytable = [40, 40, 40, 40, 80, 80, 100, 200, 300];		
		
const OCCURRENCES = [];		
for (let reel = 0; reel < reels.length; ++reel) {
	OCCURRENCES.push(occur(reels[reel]))
}	

const reducer = (accumulator, curr) => accumulator + curr;

let TOTALCOMBO = 1;
const COUNTS = new Array(9);
COUNTS.fill(1,0,9);
for (let o = 0; o < OCCURRENCES.length; ++o) {
	let values = Object.values(OCCURRENCES[o]);
	TOTALCOMBO *= values.reduce(reducer);
	for (let s = 0; s < values.length; ++s) {
		COUNTS[s] *= values[s];
	}
}
const HITS = new Array(9);
HITS.fill(0,0,9);
for (let s = 0; s < COUNTS.length; ++s) {
	HITS[s] = COUNTS[s]/TOTALCOMBO
}

let RTP=0;
const PERC = new Array(9);
PERC.fill(0,0,9);
for (let s = 0; s < HITS.length; ++s) {
	PERC[s] = HITS[s]*paytable[s];
	RTP += HITS[s]*paytable[s];
}

//0.9682158119658119
console.log(RTP);