Angularjs prevent form submission when input validation fails

Change the submit button to:

<button type="submit" ng-disabled="loginform.$invalid">Login</button>

So the suggested answer from TheHippo did not work for me, instead I ended up sending the form as a parameter to the function like so:

<form name="loginform" novalidate ng-submit="login.submit(loginForm)" class="css-form">

This makes the form available in the controller method:

$scope.login = {
    submit : function(form) {
        if(form.$valid)....
    }

Your forms are automatically put into $scope as an object. It can be accessed via $scope[formName]

Below is an example that will work with your original setup and without having to pass the form itself as a parameter in ng-submit.

var controller = function($scope) {

    $scope.login = {
        submit: function() {
            if($scope.loginform.$invalid) return false;

        }
    }

};

Working example: http://plnkr.co/edit/BEWnrP?p=preview

HTML:

<div class="control-group">
    <input class="btn" type="submit" value="Log in" ng-click="login.onSubmit($event)">
</div>

In your controller:

$scope.login = {
    onSubmit: function(event) {
        if (dataIsntValid) {
            displayErrors();
            event.preventDefault();
        }
        else {
            submitData();
        }
    }
}

Just to add to the answers above,

I was having a 2 regular buttons as shown below. (No type="submit"anywhere)

<button ng-click="clearAll();" class="btn btn-default">Clear Form</button>
<button ng-disabled="form.$invalid" ng-click="submit();"class="btn btn-primary pull-right">Submit</button>

No matter how much i tried, pressing enter once the form was valid, the "Clear Form" button was called, clearing the entire form.

As a workaround,

I had to add a dummy submit button which was disabled and hidden. And This dummy button had to be on top of all the other buttons as shown below.

<button type="submit" ng-hide="true" ng-disabled="true">Dummy</button>

<button ng-click="clearAll();" class="btn btn-default">Clear Form</button>

<button ng-disabled="form.$invalid" ng-click="submit();"class="btn btn-primary pull-right">Submit</button>

Well, my intention was never to submit on Enter, so the above given hack just works fine.

Although not a direct solution for the OPs question, if your form is within an ng-app context, but you want Angular to ignore it altogether, you can do this explicitly using the ngNonBindable directive:

<form ng-non-bindable>
  ...
</form>

I know this is an old thread but I thought I'd also make a contribution. My solution being similar to the post already marked as an answer. Some inline JavaScript checks does the trick.

ng-click="form.$invalid ? alert('Please correct the form') : saveTask(task)"

I know it's late and was answered, but I'd like to share the neat stuff I made. I created an ng-validate directive that hooks the onsubmit of the form, then it issues prevent-default if the $eval is false:

app.directive('ngValidate', function() {
  return function(scope, element, attrs) {
    if (!element.is('form'))
        throw new Error("ng-validate must be set on a form elment!");

    element.bind("submit", function(event) {
        if (!scope.$eval(attrs.ngValidate, {'$event': event}))
            event.preventDefault();
        if (!scope.$$phase)
            scope.$digest();            
    });
  };
});

In your html:

<form name="offering" method="post" action="offer" ng-validate="<boolean expression">