[SalesForce] How to replace window.open() in lightning

You can use either Window.postMessage to safely transfer data between the popup and the original window; this is the preferred method. Alternatively, you can also set an Apex Cookie that can be shared between the two windows. Using expando properties of window.opener should not be used, because you can't even verify that the receiving page is even the original page which opened the popup; this might cause undesirable behavior.

By using navigatingToURL

In Component

<aura:component implements="force:appHostable,force:lightningQuickActionWithoutHeader,flexipage:availableForAllPageTypes" access="global" >
        <ui:button label="navigateToURL" press="{!c.gotoURL}" />
</aura:component>

In controller

gotoURL : function(component, event, helper) {
    var urlEvent = $A.get("e.force:navigateToURL");
    urlEvent.setParams({
        "url":"vfpage url"
    });
    urlEvent.fire(); }