I'm trying to capture the value of a text field on an HTML form using document.getElementById(my_field).value where the variable my_field is passed to my function dynamically, but am hitting a wall.
How do you use a variable in this context?
The function just doesn't seem to parse the contents of the variable my_field, instead treating it as a string no matter whether I use quotes, square brackets or curly braces.
function myFunction() {
var my_field = arguments[0];
var current_value = document.getElementById(my_field).value;
alert ("Current Value: " + current_value);
}
I'm doing it this way because I have multiple records on a form and each row has its own unique id for the required field.
Running the above just does nothing. The alert never pops which I assume is because current_value never gets set.
To add further detail - I tried to simplify everything for the purposes of this question as there's lots of other unnecessary complications that will only detract from the main issue - on my HTML form is a text field which calls my function on onChange
onchange="enforce_multiples('quantity[<?php echo $line_id; ?>]',<?php echo $product['minimum'];?>)"
I've checked that arguments[0] and [1] are being captured correctly by outputting their values to an alert. Everything works fine up until I try to set the quantity_entered value.
<script>
function enforce_multiples() {
var line_id = arguments[0];
var quantity_increments = arguments[1];
var quantity_entered = document.getElementById([line_id]).value;
alert("QE" + quantity_entered);
//var quantity_mod = quantity_entered % quantity_increments;
//var revised_quantity = quantity_entered - quantity_mod;
//alert("RQ: " + revised_quantity);
//document.getElementById([line_id]).value = revised_quantity;
}
</script>
Checked the console and I receive the error: Uncaught TypeError: Cannot read property 'value' of null on the geElementById line
myFunc()is called, and post any errors you get on console.getElementById()— alphabetic case is important.