What does the construct x = x || y mean?

by

I am debugging some JavaScript and can’t explain what this || does:

function (title, msg) {
  var title = title || 'Error';
  var msg   = msg || 'Error on Request';
}

Why is this guy using var title = title || 'ERROR'? I sometimes see it without a var declaration as well.

12 Answers
12

Leave a Comment