use this capitalize filter

var app = angular.module('app', []);

app.controller('Ctrl', function ($scope) {
   $scope.msg = 'hello, world.';
});

app.filter('capitalize', function() {
    return function(input) {
      return (angular.isString(input) && input.length > 0) ? input.charAt(0).toUpperCase() + input.substr(1).toLowerCase() : input;
    }
});

<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.23/angular.min.js"></script>
<div ng-app="app">
    <div ng-controller="Ctrl">
        <p><b>My Text:</b> {{msg | capitalize}}</p>
    </div>
</div>

I'd say don't use angular/js as you can simply use css instead:

In your css, add the class:

.capitalize {
   text-transform: capitalize;
}

Then, simply wrap the expression (for ex) in your html:

<span class="capitalize">{{ uppercase_expression }}</span>

No js needed ;)

If you use Bootstrap, you can simply add the text-capitalize helper class:

<p class="text-capitalize">CapiTaliZed text.</p>

EDIT: just in case the link dies again:

Text Transform

Transform text in components with text capitalization classes.

lowercased text.
UPPERCASED TEXT.
CapiTaliZed Text.

<p class="text-lowercase">Lowercased text.</p>
<p class="text-uppercase">Uppercased text.</p>
<p class="text-capitalize">CapiTaliZed text.</p>

Note how text-capitalize only changes the first letter of each word, leaving the case of any other letters unaffected.