JavaScript variable is undefined after being passed in a function

Question

Hi I am working with a function and I just can't see what the problem is, help please?

This is the JavaScript function to check the length of an input.

function checkLength(o, min, max)
    {
        if ( o.val().length > max || o.val().length < min )
        {
            $("#uper_length_stud").show()
            return false;
        } 
        else
        {
            return true;
        }
    }

under it is a code which calls it.

$("#signin").click(function(e) {
       var name = $("#up_stud_fname").val(), x;
       x = checkLength(name, 3, 50);
       //other codes follow
}

It says at part o.val() that o is undefined. Though I think it is passed correctly? What seems to be the problem?

The Html part Update 更新

Answer 1

In checkLength() you have not passed any thing.

Try to pass all arguments to it

Answer 2

pass three parameters to the function

Here function wants 3 parameters ,and you are not passing it,so It says undefined

o, min, max

Answer 3

Try this One Check this fiddle http://jsfiddle.net/pratbhoir/9QTYk/

Html Code

<input id='firstName' />
<button id="btn"> Button</button>

JavaScript Code

$("#btn").click(function() {
    var name = $('#firstName').val();
    x = checkLength(name,1,4);
    //other codes follow
});


function checkLength(o, min, max)
{
    if ( o.length > max || o.length < min )
    {
        //$("#uper_length_stud").show()
        return false;
    } 
    else
    {
        return true;
    }
}

Answer 4

You can takeout the .val() from your if condition because name is a string which you are passing:

function checkLength(o, min, max){
    if ( o.length > max || o.length < min ){
        $("#uper_length_stud").show();
        return false;
    } 
}

and i think you don't need the else part and make sure that your function is in global scope.