Compare an array element to particular string of characters in javascript

It looks like you're using jQuery already, which has an $.inArray() utility method.

You should turn your list of characters into a regular expression, in my opinion:

var badchars = /[<>$@&+()[\]{},` ]/;
if (badchars.test(id_val)) {
  // contains invalid characters
}

You need to write in_array function, simple example:

function in_array( arr, val ) {
    for( var i = 0; i < arr.length; i++) {
        if( arr[ i ] == val ) {
            return true;
        }
    }
}

or using regular expressions:

if( id_val.search( /[^0-9]/g ) == -1 )

or using regex you can strip all non-numeric characters:

var id_val = $("#id_number").val(); //text field contains "mu 1$2@345"
id_val = id_val.replace( /[^0-9]/g, '' );
console.log( id_val ); //text now field contains "12345"

or if you want wo allow latin char's as well:

[^0-9A-Za-z]

^ this will not include space char as well.

You can use indexOf on arrays, but older versions of MSIE's jScript engine don't support this method natively. So either augment the Array.prototype for those browsers (not without risks, obviously), or simply use a string of chars you want to test for:

var nonoChars = '<>$@&+()[]{},`';
for(var i = 0; i< id_val.length; i++)
{
    if (nonoChars.indexOf(id_val.charAt(i)) > -1)
    {
        alert('Char #' + (i + 1) + ' is not allowed!');
        return false;
    }
}
//input ok

But, in this case, a regex simply makes more sense:

if (id_val.match(/[<>$@&+()\[\]{},`]/))
{
    alert('Invalid input');
    return false;
}
//input ok