Proxying Input Variables
Many component properties can be set either with a plain UI control, such as a checkbox, or with a JavaScript expression instead - for example, a component's Hidden property can be a simple on/off switch, or a script that decides visibility based on form data. The input variables available inside these scripts, such as contexts, data, form, and http, are not passed in as plain objects - they are wrapped in a proxy that tracks which fields the script actually reads, so Shesha only recalculates the property when a field it depends on changes.
Why Proxying Exists
Without this optimization, changing any single field would re-run the JS expression for every scripted property on every component on the form, since there would be no way to know which fields a given script actually depends on. That barely matters for a form with a handful of components, but a form with dozens of fields, tabs, and sub-forms would visibly lag on every keystroke if every scripted property recalculated on every change.
To avoid that, every input variable passed into a scripted property (data, contexts, and so on) is wrapped in a proxy. Reading a field through the proxy returns its real value and records that the script "touched" that field. The next time any field changes, Shesha only re-runs the scripts that touched it.
Example - Only firstName changes trigger recalculation:
Suppose a form has three fields, firstName, lastName, and description, and the description field's Hidden property is scripted as:
return data.firstName?.length > 3;
Because this script only ever reads data.firstName, Shesha only recalculates description's Hidden property when firstName changes. Editing lastName does not trigger it.
Working With Proxied Data Directly
Because the proxy tracks reads and writes transparently, you can work with form data and contexts directly, without needing helper methods like setFieldValue, setFieldsValue, or setFormData:
data.firstName = data.firstName + ' test';
console.log(data) or console.log(JSON.stringify(data)) logs the proxy object itself. The proxy still behaves like the real object for property access, but its printed representation looks different from a plain object.
Prior to version 0.44, you can read a variable's underlying value without going through the proxy via its _data property, for example data._data or pageContext._data. From version 0.44 onward, a hidden test.getArguments(arguments) function is available inside the executable to return the input variables unproxied.