Question

I’m doing a javascript assignment and have just learned that I can do it in jQuery if I wish, rather than vanilla javascript. I thought I’d give it a go to see what it’s like.

This is the contents of my javascript function:

    rowsArray = $("#Table1 tr");

for (i=0;i<rowsArray.length;i++){
    numSeatsInRow = rowsArray[i].getElementsByTagName("img").length;                    // discovers the number of seats in row [i]
    for(j=0;j<numSeatsInRow;j++) {                                // loops round once for each set in row [i]
 var currentSeat = rowsArray[i].getElementsByTagName("img")[j];
 currentSeat.setAttribute("id","row" + i + "Seat" + j);
 currentSeat.onmouseover = function(){this.src = "images/taken.gif"};
 currentSeat.onmouseout = function(){this.src = "images/available.gif"};
 currentSeat.onclick = function() {
      this.src = "images/mine.gif";
      this.onmouseover = null;
      this.onmouseout = null;
      document.getElementById("myTickets").innerHTML += this.id;
 }  
}

As you can see, I started converting to jQuery with the first line, but got stuck 🙂

The code works as is, but I figure there must be a more elegant way of doing it in jQuery. I tried using $.each but my selectors or syntax was wrong and it didn’t work. I have a vague idea how it works for a 1D array, but I’m not clear on how to iterate through the items in nested arrays i.e. array[x][y].

The function creates and moves through a 2D array changing the id and mouse events of a set of images.

Any thoughts would be much appreciated 🙂

Answer 1

It can be improved further, but something like this would work:

$("#Table1 tr").each(function(i) {
   $(this).find("img").each(function(j) {
     this.id = "row" + i + "Seat" + j;
     $(this).hover(function() { this.src = "images/taken.gif"; }, 
                   function() { this.src = "images/available.gif"; })
            .click(function() { 
               var img = this;
               this.src = "images/mine.gif";
               $(this).unbind("mouseenter mouseleave"); 
               $("#myTickets").html(function(i, h) { return h + img.id; });
             });
   });
});

Using .each() and the index it passes as the first parameter to the callback shortens it a bit (you don’t need your own i and j, they’re already there) the rest is just jQuery conversion, e.g. .hover() for the mouse entering/leaving and .unbind() to remove those handlers it later.

---

Here’s a bit more verbose but much more efficient version using .delegate():

$("#Table1 tr").each(function(i) {
   $(this).find("img").each(function(j) {
     this.id = "row" + i + "Seat" + j;
   });
});
$("#Table1").delegate("tr img", "click", function() { 
  var img = $(this).addClass("mine").add("src", "images/mine.gif"); 
  $("#myTickets").html(function(i, h) { return h + img.attr("id"); });
}).delegate("tr img:not(.mine)", "mouseenter", function() { 
  this.src = "images/taken.gif";
}).delegate("tr img:not(.mine)", "mouseleave", function() { 
  this.src = "images/available.gif";
});

This attaches only 3 handlers to the <table> and listens for events to bubble up, rather than attaching 3 handlers per image, so it’s much cheaper on the page load side, and and infinitesimal difference on the runtime side.