jQuery on()未定义函数

After making changes from original to changed code boxes, I now get Uncaught Type error: Undefined is not a function. Any ideas as to why? Thanks

Original:

 $('.comment').click(function(e){
    alert("click");
    e.preventDefault();
    $(".slidingDiv2").slideToggle();
});   

Changed:

 $(document.body).on('click', '.comment' ,function(){
        alert("click");
        e.preventDefault();
        $(".slidingDiv2").slideToggle();
    });

Easiest way might be to set it to display:none in your css, so it is hidden until your click event ( $('.comment').click(function(e){... ) is fired.

CSS:

.slidingDiv2 {
    display:none;
}

$(document.body) is not a valid selector, use $('body')