javascript function works without argument,

Question

function change_tag(url){
 $('.filter_button_confirm').unbind('click').on('click', function(){
 ...
 console.log(url);
 $.ajax({
 url: url,
 type: 'POST',
 data: {
 ...
 },
 beforeSend: function(){
 ...
 }
 })
 .done(function(data){
 ...
 })
 });
};

When I call the function with argument change_tag('/some_url/') of course it works.

But, change_tag() also works perfectly.

It brings data from the url that I set in the past.

console.log(url) shows 'undefined' so I don't know how it knows the url.

• James Monger: What do you want the solution to be? Should the code throw an error if no url is given?
• Fabien: What if you rename your parameter 'url', to check if you are not using a global variable ?
• j08691: Did you declare url globally?
• atom Jung: I want to know how it works. I'm afraid error occurs later.

Answer 1

Since you're not passing in a parameter to the function, url is undefined and so the ajax call gets called with url: undefined. This is the same as not providing an url, and makes it post to the url you're currently on.

For more info you can check the jQuery page: http://api.jquery.com/jquery.ajax/

• James Monger: Calling change_tag() actually calls change_tag with url as undefined, not null.
• j08691: But the OP says that the console log shows undefined for the URL and adds that "It brings data from the url that I set in the past.", not the current URL