表单禁止回车提交的js代码

document.onkeydown = function(event) {  
            var target, code, tag;  
            if (!event) {  
                event = window.event; //针对ie浏览器  
                target = event.srcElement;  
                code = event.keyCode;  
                if (code == 13) {  
                    tag = target.tagName;  
                    if (tag == "TEXTAREA") { return true; }  
                    else { return false; }  
                }  
            }  
            else {  
                target = event.target; //针对遵循w3c标准的浏览器，如Firefox  
                code = event.keyCode;  
                if (code == 13) {  
                    tag = target.tagName;  
                    if (tag == "INPUT") { return false; }  
                    else { return true; }   
                }  
            }  
        };