preventDefault（）不在输入类型文本中工作

Question

This is my code:

$('#Login').keydown(function(e){         
        if(e.which  == 32){     
            alert("enter");
            this.preventDefault();            
        }        
    });

This code doesn't work but sends the alert

$('#Pwd,#Pwd2').on('keydown',function(e){
        if(e.which == 32){
            e.preventDefault();
        }
    });

And this code works. I do not understand why.

Answer 1

You are wanting to prevent the default action of the Event (which is passed in as the parameter for your event function, you are calling it e ).

this is the element that is the target of your event (ie: in this case e.target which will be your #Login element) and not an event itself, this does not have a preventDefault() .

Just use the Event object for this as well:

$('#Login').keydown(function(e){         
    if(e.which == 32){     
        e.preventDefault();            
    }        
});

With the above you'll see the event is cancelled every time you hit the space bar within #Login : http://jsfiddle.net/xWmUU/

Answer 2

preventDefault is a method of the Event object, so it makes sense that it works when called on an event.

this will refer to #Login in this case, which is a DOM object and will not have the preventDefault method.

Note that because of how event propagation works, this will not always be equal to e.target .