How to display placeholders in AngularJS for undefined expression values?

Question

If I have an expression {{ x }} and x is undefined or null, then how can I display a placeholder for it?

I provided one solution

Answer 1

Implement default filter:

app.filter('default', function(){
  return function(value, def) {
    return (value === undefined || value === null? def : value);
  };
});

And use it as:

{{ x | default: '?' }}

The advantage of the filter solution over {{ x || '?'}} is that you can distinguish between undefined, null or 0.