Jam.py documentation



domain: client

language: javascript

class Item class


Write an on_before_field_changed event handler to implement any special processing before field’s data has been changed.

The field parameter is the field whose data is about to be changed. To get the item that owns the field, use the owner attribute of the field.

Before triggering this event handler the application assigns the new value that is about to be set to the new_value attribute to of the field. You can change the value of this attribute. This value will be used to change field’s data.


function on_before_field_changed(field) {
    if (field.field_name === 'quantity' && field.new_value < 0) {
        field.new_value = 0;