Convert javascript array handling to jQuery

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 :)

Nick Craver · Accepted Answer · 2010-10-07 16:51:15Z

2

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.

edited Oct 7, 2010 at 16:51

answered Oct 7, 2010 at 16:35

Nick Craver

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5 Comments

Sean Vieira Over a year ago

how are i and j getting updated here? I feel like I'm missing something.

Nick Craver Over a year ago

@Sean - They're the arguments passed to the callbacks, function(i) {, the callback for .each() has the signature of function(index, element).

Sean Vieira Over a year ago

Smacks head @Nick -- I'd completely forgotten about that; thanks for the reminder!

John Fisher Over a year ago

+1 for the delegate suggestion. I use them all the time and they greatly improve performance in screens with bunches of data.

melat0nin Over a year ago

Thanks, that looks great. I'm going to go with John's simpler answer below though, because it's closer to my understanding of

John Fisher · Accepted Answer · 2010-10-07 16:31:57Z

This is untested, but should give you what you need to get things working.

rowsArray = $("#Table1 tr"); 

for (i=0;i<rowsArray.length;i++){ 
    var images = rowsArray.eq(i).find("img");
    numSeatsInRow = images.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 = images.eq(j); 
 currentSeat.attr("id","row" + i + "Seat" + j); 
 currentSeat.mouseover(function(){this.src = "images/taken.gif"}); 
 currentSeat.mouseout(function(){this.src = "images/available.gif"}); 
 currentSeat.click(function() { 
      var self = $(this);
      self.attr("src", "images/mine.gif"); 
      self.unbind("mouseover");
      self.unbind("mouseout");
      $("#myTickets").html(this.id); 
 });   
}

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