How to pass JavaScript variable to jQuery ajax request

Question

I am trying to pass a variable to an jquery ajax request:

$(document).ready(function() {
            // get page number
            var page = parseInt(getUrlParameter('page'));
            if (page < 1) page = 1;
            var page_next = page + 1;

          $.ajax({
                type: "GET",
                data: { 
                    page: page,

                },  
                dataType: 'json', 
           ...

unfortunatelly the variable "page" seems not to be present inside the ajax request. Doing an cosole.log(page); inside reveils "NaN" as a value.

The problem seems to be

if (page < 1) page = 1;

If this value retrieved via get is not present, then page will be NoN.

How can I make sure page is always defined as minimum 1 ?

Answer 1

Your getUrlParameter is returning something that is not convertible to a number NaN = Not a Number , if you share that function maybe we can debug a little bit further the root cause of your issue, in the meantime, I suggest the following validation:

var page = parseInt(getUrlParameter('page'));
if (page < 1 || isNaN(page)) page = 1;
var page_next = page + 1;

That way if your page is not a number, you default it to page 1. Hope this clears things out and helps you.

Answer 2

If your problem is within the if statement, the fastest solution I can think about (despite I don't approve it) is this one:

Replace :

var page = parseInt(getUrlParameter('page'));

with:

var page = +getUrlParameter("page") || 1;

if page is falsey (NaN is falsey) it will set it to 1, else to its result.

Example with fiddle:

function getUrlParameter ( param ) {
    return param === "page" ? 5 : false;
}

var page = +getUrlParameter("hello") || 1;
alert(page);

page = +getUrlParameter("page") || 1;
alert(page);

http://jsfiddle.net/51tvdsve/

In any case, you should rather try to fix your getUrlParameter function instead of trying to avoid its output, but that's just my opinion.