JavaScript code to stop form submission

One way to stop form submission is to return false from your JavaScript function.

When the submit button is clicked, a validation function is called. I have a case in form validation. If that condition is met I call a function named returnToPreviousPage();

function returnToPreviousPage() {
    window.history.back();
}

I am using JavaScript and Dojo Toolkit.

Rather going back to the previous page, it submits the form. How can I abort this submission and return to the previous page?