Get nested value from an object using a key path. Supports keys with `dots` in the path.

script.js

function splitPath(path) {
  const paths = [];

  for (let i = 0; i < path.length; i++) {
    const c = path[i];

    if (c === ']') {
      continue;
    }

    if (i === 0) {
      let end = i + 1;
      let char = path[end];
      while (true) {
        char = path[end];

        if (char === '.' || char === '[') {
          break;
        }
        end++;
      }
      paths.push(path.slice(i, end).replaceAll(/["']/g, ''));
      i = end - 1;
      continue;
    }

    if (c === '[') {
      let end = i + 1;
      let char = path[end];
      while (true) {
        char = path[end];

        if (char === ']') {
          break;
        }
        end++;
      }
      paths.push(path.slice(i + 1, end).replaceAll(/["']/g, ''));

      i = end - 1;
      continue;
    }

    if (c === '.') {
      let end = i + 1;
      let char = path[end];
      let isEnd = end === path.length - 1;
      while (true) {
        char = path[end];

        if (char === '.' || char === '[' || end === path.length - 1) {
          break;
        }
        end++;
        isEnd = end === path.length - 1;
      }

      if (i + 1 === end) {
        paths.push(path.slice(i + 1, end + 1).replaceAll(/["']/g, ''));
      } else if (isEnd) {
        paths.push(path.slice(i + 1, end + 1).replaceAll(/["']/g, ''));
      } else {
        paths.push(path.slice(i + 1, end).replaceAll(/["']/g, ''));
      }
      i = end - 1;
      continue;
    }
  }

  return paths;
}

/**
 * Supports
 * a.b.c.0.abc['ss'].a[4].xyz['key.with.a.dot.in.its.name']['path'][23]
 */
function select(payload, keyPath) {
  let ref = payload;

  const keys = splitPath(keyPath);

  for (const key of keys) {
    ref = isNaN(key) ? ref[key] : ref[Number(key)];
  }

  return ref;
}

Example

select({ a: { b: [ { c: [ { d: { 'v.b': 2 } } ] } ] }  }, "a.b.0.c.0.d['v.b']"); // 2