Function JS_SetPropertyById 

pub unsafe extern "C" fn JS_SetPropertyById(
    cx: *mut JSContext,
    obj: Handle<*mut JSObject>,
    id: Handle<PropertyKey>,
    v: Handle<Value>,
) -> bool

Perform the assignment obj[id] = v.

This function performs non-strict assignment, so if the property is read-only, nothing happens and no error is thrown.