I have a text input and I don't want to allow users to use spaces, and everything typed will be turned into lowercase.
I know I'm not allowed to use filters on ng-model eg.
ng-model='tags | lowercase | no_spaces'
I would suggest to watch model value and update it upon chage: http://plnkr.co/edit/Mb0uRyIIv1eK8nTg3Qng?p=preview
The only interesting issue is with spaces: In AngularJS 1.0.3 ng-model on input automatically trims string, so it does not detect that model was changed if you add spaces at the end or at start (so spaces are not automatically removed by my code). But in 1.1.1 there is 'ng-trim' directive that allows to disable this functionality (commit). So I've decided to use 1.1.1 to achieve exact functionality you described in your question.