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

5.4 Dominant writing direction

Write a function that computes the dominant writing direction in a string of text. Remember that each script object has a direction property that can be "ltr" (left-to-right), "rtl" (right-to-left), or "ttb" (top-to-bottom).

The dominant direction is the direction of a majority of the characters which have a script associated with them. The characterScript and countBy functions defined earlier in the chapter are probably useful here.

Hints

Your solution might look a lot like the first half of the textScripts example. You again have to count characters by a criterion based on characterScript, and then filter out the part of the result that refers to uninteresting (script-less characters).

Finding the direction with the highest character count can be done with reduce. If it’s not clear how, refer back to the example earlier in the chapter, where reduce was used to find the script with the most characters.

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