闭包

<div id="divTest">
        <span>0</span> <span>1</span> <span>2</span> <span>3</span>
    </div>
    <div id="divTest2">
        <span>0</span> <span>1</span> <span>2</span> <span>3</span>
    </div>

$(document).ready(function() {
            var spans = $("#divTest span");
            for (var i = 0; i < spans.length; i++) {
                spans[i].onclick = function() {
                    alert(i);
                }
            }
        });

var spans2 = $("#divTest2 span");
        $(document).ready(function() {
            for (var i = 0; i < spans2.length; i++) {
                (function(num) {
                    spans2[i].onclick = function() {
                        alert(num);
                    }
                })(i);
            }
        });