为什么验证功能在页面刷新后调用而单击时什么也没有发生

Question

var asign = function(id){

 return document.getElementById(id) ;
 } ;

var f_name = asign('fname').value ;

 var validate = function (a) {
this.a = a ;
    if(!a){
        alert("Somthing is require");
    }  else if(a.length<6){
        alert("characters should be minimum 6") ;
    }
}  


 asign('submit').addEventListener('click',validate(f_name),false) ;

validate function invoke in page refresh and after click the button nothing happen validate function nothing happen

Answer 1

You need pass reference to function as a argument in addEventListener but not call it,

1 .you can wrap your code to function like this

asign('submit').addEventListener('click', function () {
  validate();
}, false);

2 .or use .bind

asign('submit').addEventListener('click', validate.bind({}), false);

Example

 var asign = function(id) { return document.getElementById(id); }; var validate = function () { var a = asign('fname').value; if (!a) { alert("Somthing is require"); } else if (a.length < 6) { alert("characters should be minimum 6"); } } asign('submit').addEventListener('click', validate.bind({}), false); 

 <input id="fname"> <button id="submit">submit</button>