Default value

[Hurtak]

I don't think it's good to recommend using || for setting default value to variables. It's nice shortcut but it can cause trouble when valid input (0, false, '') is converted to default value. I would recommend mentioning explicitly these dangers in that chapter or add chapter about more safe default value assigning

function example(value) {
  if (typeof value === 'undefined') {
    value = 'defaultValue';
  }
}

[bevacqua]

You can always add the recommendation in a pull request. I'd advice against the typeof check, I prefer comparing against void 0 for brevity.

[Hurtak]

Why would you advice against typeof check?

[bevacqua]

brevity