js:
function check(){
var a =document.getElementById("email");
if(a.length==0){alert("111111");}
else{alert("222222");}
}html:<input type="text" id="email"/>
<input type="button" value="13221321" onclick="return check()" id="button"/>为什么即使email为空,都是运行"2222222",
function check(){
var a =document.getElementById("email");
if(a.length==0){alert("111111");}
else{alert("222222");}
}html:<input type="text" id="email"/>
<input type="button" value="13221321" onclick="return check()" id="button"/>为什么即使email为空,都是运行"2222222",
获取的值不一样
function check(){
var a =document.getElementById("email").value;
if(a.length==0){alert("111111");}
else{alert("222222");}
}
var emailvalue = a.value; if(emailvalue.length==0){alert("111111");}
else{alert("222222");}
}