something

something.js

const limits = [
  { "x<": [90, 8] },
  { "x<": [80, 7.9] },
];

const re = /^x?([<>]=?)$|^([<>]=?)x$/i;
const comparators = {
  "<": (a, b) => a < b,
  "<=": (a, b) => a <= b,
  ">": (a, b) => a > b,
  ">=": (a, b) => a >= b,
};
const callers = [
  (fn, a, b) => fn(b, a),
  (fn, a, b) => fn(a, b),
];

function getFirstKey(obj) {
  for (const key in obj) return key;
  throw new TypeError("Empty object");
}

function processMatch(slice) {
  const idx = slice[0] == null ? 1 : 0;
  return { caller: callers[idx], comparator: comparators[slice[idx]] };
}

function parser(obj) {
  const key = getFirstKey(obj);
  const { 0: limit, 1: value } = obj[key];
  const match = key.match(re);
  if (match == null) throw new TypeError("Invalid key");
  const { caller, comparator } = processMatch(match.slice(1));
  return function(element) {
    if (caller(comparator, limit, element)) {
      this.value = value;
      return true;
    }
  };
}