manipulating input values

aalexaa · 03-26-2010, 08:42 AM

I have the following code:

Code:

<html>
<head>
<script type="text/javascript">
function copyValue()
{
var x= document.getElementById("fname").value;
var y =document.getElementById("dname").value;
x = y;
}
</script>
</head>

<body>
<input type="text" id="dname" onChange="copyValue()" />
Enter your name: <input type="text" id="fname" />
</body>

</html>

and it won't work.
but when i add an extra line, alert(x+" "+y) to tell me what the value of each input is, both values are the same. but the text won't show up in the second input field.

my goal here is to have the second input field change to whatever the first one says after i've typed something.
any suggestions?

Dormilich · 03-26-2010, 10:11 AM

Quote:

Originally Posted by aalexaa

and it won't work.
but when i add an extra line, alert(x+" "+y) to tell me what the value of each input is, both values are the same. but the text won't show up in the second input field.

well, it does work, just not the way you think it works.

in general, everything besides the primitives is passed by reference*, thus in the beginning x and y point to the two input’s value attributes. when you do x = y x points now to the same value attribute as y, without doing anything to the previous assigned value.

PHP Code:


			
function copyValue()
{
    var x = document.getElementById("fname");
    var y = document.getElementById("dname");
    x.value = y.value;
}

* - can be annoying when working with arrays

Kor · 03-26-2010, 12:39 PM

Quote:

Originally Posted by Dormilich

* - can be annoying when working with arrays

How's that?

Dormilich · 03-26-2010, 01:00 PM

example

PHP Code:


			
// …
    do {
        values = this.scramble(arr);
    }
    while (this.unsolvable(values));
// …


MagicSquare.prototype.scramble = function (a)
{
    var i, index, b = c = [];

// if I don’t hardcopy the array here, the array 
// in the calling function (arr) becomes [] and thus
// unuseable in the next cycle (if any)
    for (i = a.length; i--;) {
        c[i] = a[i];
    }
    for (i = c.length; i--;) {
        index = Math.round(Math.random() * 100 * i) % i;
        b.push(c.splice(index, 1)[0]);
    }
    return b;
};

aalexaa · 03-27-2010, 08:20 AM

Quote:

Originally Posted by Dormilich

well, it does work, just not the way you think it works.

in general, everything besides the primitives is passed by reference*, thus in the beginning x and y point to the two input’s value attributes. when you do x = y x points now to the same value attribute as y, without doing anything to the previous assigned value.

PHP Code:


			
function copyValue()

{

    var x = document.getElementById("fname");

    var y = document.getElementById("dname");

    x.value = y.value;

}

* - can be annoying when working with arrays

wow it worked! thank you.

who knew it was such a simple mistake...

Dormilich · 03-27-2010, 09:54 AM

Quote:

Originally Posted by aalexaa

who knew it was such a simple mistake...

well, it is always that simple, once you got the hang of it …