js code to limit the input of N characters in the text box_form effects

So what you have to do is
1. First distinguish whether it is a two-byte character or a one-byte character;
2. Use charCodeAt and String.fromCharCode to convert each other.
The code is as follows:

Copy code The code is as follows:

function validatePostponeValue(obj, objLength )
{
var executeResult = false;
var value = obj.value;
var byteLen=0,len=value.length;
var newValue = "";
if (value)
{
for(var i=0; i {
if(value.charCodeAt(i) > 255)
{
byteLen = 2;
if(byteLen <= 18)
{
//alert(String.fromCharCode(value.charCodeAt(i)));
newValue = String.fromCharCode(value.charCodeAt (i));
}
}
else
{
byteLen ;
if(byteLen <= 19)
{
//alert(String. fromCharCode(value.charCodeAt(i)));
newValue = String.fromCharCode(value.charCodeAt(i));
}
}
}
}

if(byteLen <= 0)
{
//alert("Cannot be empty!");
obj.focus();
}
else if(byteLen > objLength )
{
alert("You can only enter up to ten Chinese characters (20 characters).");
obj.focus();
obj.value = newValue;//value.substr (0, objLength -1);
　 }
else
{
executeResult = true;
}

return executeResult;
}