Question

Can I pass a value out of a javascript function and back to the calling function, e.g.

function updateURL(url, name, param) {
  url = url + "&" + name + "=" + param;
}

I want to update url and return the new value.

Is this possible?

Answer 1

What you’re asking for is called “pass-by-reference“. Javascript uses “pass-by-value” for the native types (int, string, etc)—other types are pass-by-reference. For your specific case, I can think of two ways to get what you want. The first is to require callers to pass in an array with a single element and modify that element:

function updateURL(url, name, param) {
    url[0] = url[0] + "&" + name + "=" + param;
}
url = ['http://www.google.com/?'];
updateURL(url, 'foo', 'bar');
alert(url[0]);

The second method would be to use an attribute on an object:

function updateURL(url, name, param) {
    url.url = url.url + "&" + name + "=" + param;
}
url = new Object();
url.url = 'http://www.google.com/?';
updateURL(url, 'foo', 'bar');
alert(url.url);