Is it possible to call a Lightning Component from a Javascript function?

There is an event named force:navigateToComponent. You can use this event for going to another component. It is currently in the Beta version in the Winter '17 release.

Example:

var evt = $A.get("e.force:navigateToComponent");
    evt.setParams({
        componentDef: "c:componentName",
        componentAttributes: {
            // Attributes here.
        }
    });
evt.fire(); 

Source: https://resources.docs.salesforce.com/sfdc/pdf/lightning.pdf (Page number 411 in the document)