window.onload =function() {  
        document.getElementByIdx_x_x("test").onkeyup =function() {  
            this.value =this.value.replace(/\s/g,'').replace(/(\d{4})(?=\d)/g,"$1 ");;  
        };  
    };  

转载请注明：有爱前端 » JS 输入银行卡号，4位自动加空格(转)