Humanize a string in JavaScript

How do I humanize a string? Based on the following criteria:

• Deletes leading underscores, if any.
• Replaces underscores with spaces, if any.
• Capitalizes the first word.

For example:

this is a test -> This is a test
foo Bar Baz    -> Foo bar baz
foo_bar        -> Foo bar
foo_bar_baz    -> Foo bar baz
foo-bar        -> Foo-bar
fooBarBaz      -> FooBarBaz

Best is indeed to use some regexes:

^[\s_]+|[\s_]+$ catches 1 or more white-space characters or underscores either at the very beginning (^) or at the very end ($) of the string. Note that this also catches new-line characters. Replace them with an empty string.

[_\s]+ Again catches 1 or more white-space characters or underscores, since the ones at the beginning/end of the string are gone, replace with 1 space.

^[a-z] Catch a lowercase letter at the beginning of the string. Replace with the uppercase version of the match (you need a callback function for that).

Combined:

function humanize(str) {
  return str
      .replace(/^[\s_]+|[\s_]+$/g, '')
      .replace(/[_\s]+/g, ' ')
      .replace(/^[a-z]/, function(m) { return m.toUpperCase(); });
}

document.getElementById('out').value = [
  '    this is a test',
  'foo Bar Baz',
  'foo_bar',
  'foo-bar',
  'fooBarBaz',
  '_fooBarBaz____',
  '_alpha',
  'hello_ _world,   how    are________you?  '
].map(humanize).join('\n');

textarea { width:100%; }

<textarea id="out" rows="10"></textarea>