A function to easily sort JS objects by key.

sortBy.js

/**
 * Create a sorting function that can sort objects by a calculated key. Can be passed to `Array.sort`.
 * @param cb A function that will be passed each object and expected to return a key to sort by.
 *  The key can be either a string, number, or an array of those.
 * @return A function that can be passed to `Array.sort`.
 */
function sortBy(cb) {
  const stringCompare = (a, b) => a.localeCompare(b);
  
  const numberCompare = (a, b) => a - b;
  
  const arrayCompare = (a, b) => {
    let result = 0;
    for (let i = 0; i < a.length; ++i) {
      const aVal = a[i];
      const bVal = b[i];
      result = compare(aVal, bVal);
      if (result !== 0) {
        return result;
      }
    }
    return result;
  }
  
  const compare = (a, b) => {
    if (typeof a === 'string') {
      return stringCompare(a, b);
    }
    if (typeof a === 'number') {
      return numberCompare(a, b);
    }
    if (Array.isArray(a)) {
      return arrayCompare(a, b); 
    }
    throw new Error('Cannot compare objects of type ' + typeof a);
  }
  
  const getKey = typeof cb === 'string'
    ? a => a[cb]
    : cb;
  
  return (a, b) => compare(getKey(a), getKey(b));
}