Convert string to Pascal Case (aka UpperCamelCase) in Javascript

s = s.replace(/(\w)(\w*)/g,
        function(g0,g1,g2){return g1.toUpperCase() + g2.toLowerCase();});

The regex finds words (here defined using \w - alphanumerics and underscores), and separates them to two groups - first letter and rest of the word. It then uses a function as a callback to set the proper case.

Example: http://jsbin.com/uvase

Alternately, this will also work - a little less regex and more string manipulation:

s = s.replace(/\w+/g,
        function(w){return w[0].toUpperCase() + w.slice(1).toLowerCase();});

I should add this isn't pascal case at all, since you have word barriers (helloworld vs hello-world). Without them, the problem is almost unsolvable, even with a dictionary. This is more commonly called Title Case, though it doesn't handle words like "FBI", "the" or "McDonalds".

Here's my suggestion:

function toPascalCase(string) {
  return `${string}`
    .toLowerCase()
    .replace(new RegExp(/[-_]+/, 'g'), ' ')
    .replace(new RegExp(/[^\w\s]/, 'g'), '')
    .replace(
      new RegExp(/\s+(.)(\w*)/, 'g'),
      ($1, $2, $3) => `${$2.toUpperCase() + $3}`
    )
    .replace(new RegExp(/\w/), s => s.toUpperCase());
}

or

String.prototype.toPascalCase = function() {
  return this
    .toLowerCase()
    .replace(new RegExp(/[-_]+/, 'g'), ' ')
    .replace(new RegExp(/[^\w\s]/, 'g'), '')
    .replace(
      new RegExp(/\s+(.)(\w*)/, 'g'),
      ($1, $2, $3) => `${$2.toUpperCase() + $3}`
    )
    .replace(new RegExp(/\w/), s => s.toUpperCase());
};

Test cases:

describe('String to pascal case', function() {
  it('should return a pascal cased string', function() {
    chai.assert.equal(toPascalCase('foo bar'), 'FooBar');
    chai.assert.equal(toPascalCase('Foo Bar'), 'FooBar');
    chai.assert.equal(toPascalCase('fooBar'), 'FooBar');
    chai.assert.equal(toPascalCase('FooBar'), 'FooBar');
    chai.assert.equal(toPascalCase('--foo-bar--'), 'FooBar');
    chai.assert.equal(toPascalCase('__FOO_BAR__'), 'FooBar');
    chai.assert.equal(toPascalCase('!--foo-¿?-bar--121-**%'), 'FooBar121');
    chai.assert.equal(toPascalCase('Here i am'), 'HereIAm');
    chai.assert.equal(toPascalCase('FOO BAR'), 'FooBar');
  });
});