Question

UPDATE 1:

Here is more of the script:

$(".favorites").sortable(
    {update:function() {

    var that = this;

    var urls = ""; 
    var texts = "";

    $.map($(".favorites a"), function(elt) { 
        urls += "url=" + elt.href + "&";
        texts += "text=" + $(elt).html() + "&"; 
    }); 

    $.ajax({
        url: 'favorites.asmx/save',
        type: 'POST',
        data: { strItems:$(that).sortable("serialize",{key:'item'}), strURLs:urls.substr(0,urls.length - 1), strTexts:texts.substr(0,texts.length - 1) },
        error: function(xhr, status, error) {
                    console.log(xhr.responseText); 
        },
        success: function() {
            console.log("Values sent:- strURLs: " + urls.substr(0,urls.length - 1));
        }
    });

ORIGINAL QUESTION:

I have the following script which works, but I don’t understand it:

$.map($(".favorites a"), function(elt) { 
    urls += "url=" + elt.href + "&";
    texts += "text=" + $(elt).html() + "&"; 
}); 

I understand the basic examples in this link: http://api.jquery.com/jQuery.map/, but I don’t understand the script I have posted above.

Answer 1

The purpose of map is to create an array by taking each of the elements of the array or object you pass into it and filtering them through the function you give it; the function’s return values are collected together into the resulting array, which is the return value of map.

That code isn’t doing that. It’s not returning anything from the iterator, and it’s not using the resultant array. Basically it’s just re-invented .each by abusing map. That script should be:

$(".favorites a").each(function() { 
    urls += "url=" + this.href + "&";
    texts += "text=" + $(this).html() + "&"; 
});

(Note that I’m assuming here that urls and texts have been declared and initialized prior to the code you quoted.)

Here’s an example of a correct use of map:

var hrefs = $.map($(".favorites a"), function(elt) {
    return elt.href;
});
// hrefs is now an array containing the `href`s of all of the links