Function to sort an array of objects by a particular key's value.

sort_by_key_value.js

function sort_by_key_value(arr, key) {
  var to_s = Object.prototype.toString;
  var valid_arr = to_s.call(arr) === '[object Array]';
  var valid_key = typeof key === 'string';

  if (!valid_arr || !valid_key) {
    return;
  }

  arr = arr.slice();

  return arr.sort(function(a, b) {
    var a_key = String(a[key]);
    var b_key = String(b[key]);
    var n = a_key - b_key;
    return !isNaN(n) ? n : a_key.localeCompare(b_key);
  });
}

/*
  Used like this...
*/

var old_arr = [
  {
    test: 'betty'
  },
  {
    test: 2
  },
  {
    test: 'alfred'
  },
  {
    test: 'Chris'
  },
  {
    test: 1
  },
  {
    test: 'Betty'
  },
  {
    test: 3
  },
  {
    test: 'Alfred'
  },
  {
    test: 'chris'
  }
];

var new_arr = sort_by_key_value(old_arr, 'test');

new_arr.forEach(function(item) {
  console.log(item.test);
});

/*
  Returns...

  [
    {
      test: 1
    },
    {
      test: 2
    },
    {
      test: 3
    },
    {
      test: 'alfred'
    },
    {
      test: 'Alfred'
    },
    {
      test: 'betty'
    },
    {
      test: 'Betty'
    },
    {
      test: 'chris'
    },
    {
      test: 'Chris'
    }
  ]
*/

For what it's worth, here are examples of how Underscore (and Lo-Dash) handle this particular test array:

Passing in numbers/strings (no resulting sort, same as input)…

http://cl.ly/image/001B1H1Y0W2j

Passing in all strings (sorted, but not kept alphabetical)…

http://cl.ly/image/2W050F3s2X0k

I'm just pointing that out since a few people have asked "Doesn't Underscore (or Lo-Dash) do that?"

Answer:

No, they don't. However, I wouldn't expect them to.

This is for sorting data to be displayed in an HTML <table>, which is by its nature sort of a kludge anyway.

UPDATE

Courtesy of a coworker, you could do this in Underscore (or Lo-Dash) by passing a custom iterator function.

function sort_by_key_value(arr, key) {
  return _.sortBy(arr, function(item) {
    return String(item[key]).toLowerCase();
  });
}

var new_arr = sort_by_key_value(old_arr, 'test');

new_arr.forEach(function(item) { 
  console.log(item.test);
});

That gets 99% there, except that lowercase variations of words don't necessarily precede their uppercase counterparts…

http://cl.ly/image/272e2h0R0512

Note:

"alfred" precedes "Alfred" and "betty" precedes "Betty", yet "Chris" precedes "chris".