How to pass JavaScript variables as parameters to JSF action method?

If you use PrimeFaces, you can use a hidden input field linked to a managed bean, and you can initialize its value using javascript, for PrimeFaces, the PF function can be used to access a widget variable linked to the hidden input, in this way:

<script type="text/javascript">
function getVars() {
    // ...
    var x = locationInfo.lng; 
    var y = locationInfo.lat;
    PF('wvx').jq.val( lat1 );
    PF('wvy').jq.val( lng1 );
}
</script>

<p:inputText type="hidden" widgetVar="wvx" value="#{bean.x}" />
<p:inputText type="hidden" widgetVar="wvy" value="#{bean.y}" />

Let JS set them as hidden input values in the same form.

<h:form id="formId">
    <h:inputHidden id="x" value="#{bean.x}" />
    <h:inputHidden id="y" value="#{bean.y}" />
    <h:commandButton value="submit" onclick="getVars()" action="#{bean.submit}" />
</h:form>

function getVars() {
    // ...
    var x = locationInfo.lng; 
    var y = locationInfo.lat;

    document.getElementById("formId:x").value = x;
    document.getElementById("formId:y").value = y;
}

The command button action method could just access them as bean properties the usual way.

private int x;
private int y;

public void submit() {
    System.out.println("x: " + x);
    System.out.println("y: " + y);
    // ...
}

// Getters+setters.

An alternative is to use OmniFaces <o:commandScript> or PrimeFaces <p:remoteCommand> instead of <h:commandButton>. See also a.o. How to invoke a JSF managed bean on a HTML DOM event using native JavaScript?