What do two vertical lines in an object value mean in javascript? [duplicate]

Answer 1

The way the operator || is evaluated is that if the first part is true-ish, it returned it. If the first part is false-ish, it returns the second. The above expressions is therefore equivalent to:

if ($(el).data('start')) {
  time = $(el).data('start');
} else {
  time = new Date();
}