5.4 Dominant writing direction (Eloquent JavaScript Solutions)

5-4 Eloquent Javascript Solutions.js

// 5.4 Dominant Writing Direction

function characterScript(code) {
  for (let script of SCRIPTS) {
    if (script.ranges.some(([from, to]) => code >= from &&
                                           code < to)) {
      return script;
    }
  }
  return null;
}

function countBy(items, groupName) {
  let counts = [];
  for (let item of items) {
    let name = groupName(item);
    let known = counts.findIndex(c => c.name == name);
    if (known == -1) {
      counts.push({name, count: 1});
    } else {
      counts[known].count++;
    }
  }
  return counts;
}

function dominantDirection(text) {
  let scripts = countBy(text, char => {
    let script = characterScript(char.codePointAt(0));
    return script ? script.direction : "none";
  }).filter(({name}) => name != "none");
  switch (scripts.length) {
    case 0:
      return 'no dominant direction found';
    case 1:
      return scripts[0].name;
    default:
      if (scripts.reduce((acc, cur) => acc.count === cur.count)) {
        return 'no dominant direction found';
      } else {
        return scripts.reduce((acc, cur) => acc.count >= cur.count ? acc.name : cur.name);
      }
  }
}

console.log(dominantDirection("Hello!"));
// → ltr
console.log(dominantDirection("Hey, مساء الخير"));
// → rtl
console.log(dominantDirection(""));
// → no dominant direction found
console.log(dominantDirection("Heyخير"));
// → no dominant direction found

I found this chapter and example super boring. Your answer helped thanks.