.params到底是什么，它有什么作用？

Question

I'm currently working my way through Learning jQuery 4th edition, where i am given an example of a form which accepts one text input.The form, when submitted, searches through the jQuery docs for the string inputted, retrieves it as a JSONP object and displays it.

In the example, i am given the following code extract

//more code

  var buildItem = function(item) {
    var title = item.name,
        args = [],
        output = '<li>';

    if (item.type == 'method' || !item.type) {
      if (item.signatures[0].params) {
        $.each(item.signatures[0].params, function(index, val) {
          args.push(val.name);
        });
      }
      title = (/^jQuery|deferred/).test(title) ? title : '.' + title;
      title += '(' + args.join(', ') + ')';
    } else if (item.type == 'selector') {
      title += ' selector';
    }
    output += '<h3><a href="' + item.url + '">' + title + '</a></h3>';
    output += '<div>' + item.desc + '</div>';
    output += '</li>';

    return output;
  };

//more code

i am having trouble understanding the line

 $.each(item.signatures[0].params, function(index, val) {
              args.push(val.name);
            });

specifically what does .params actually do? I understand that it is accessing .params from within the signatures in the object returned, but i do not see any .params in the returned object, nor can i seem to find any documentation on .params ..

Any help would be appreciated.

jsFiddle can be found here: http://jsfiddle.net/QPR4Z/2/

Answer 1

See the value in signatures[0] - note that it is arbitrary data from a JSON request [for the jQuery API documentation]. That is, ".params" doesn't do anything, except function as normal property access. Despite syntax highlighting, it is not a reserved word and has no special meaning.

---

Here is some relevant extracted JSON to illustrate the point:

"signatures":[
  { //  <-- i.e. signatures[0]
    "added":"1.8",
    "params":[    // <-- property called "params", which represents an array
                  //     of objects that describe the given parameter
      {"name":"selector","type":"Selector",..}
    ],
    ..
  },
  ..
]