How to pass a parameter from js to Apex through visual force page?

In the Apex class, to get a parameter from a visual page is very easy, firstly, let’s have a look at how to pass a parameter in the Http request in js:

window.open('/apex/ExportRepaymentDetails?id=xxxx&type=create');

Then forward the parameter to the Apex class in the visual page according to the following way:

<apex:page controller="RepaymentDetails" action="{!InitParameter}" renderAs="pdf">
// ...
</apex:page>

Then get the parameter in Apex class, as the following code:

public class RepaymentDetails {
    private static string Id = '';
    private static string Type = '';
    // .....
    public static void InitParameter() {
        Id = ApexPages.CurrentPage().getParameters().get('id');
        Type = ApexPages.CurrentPage().getParameters().get('type');
    }
    // ........
}