LockerService seems to be blocking adding new properties to JS objects in LWC [duplicate]

Question

I am facing issue with LWC, probably connected to the LockerService's Proxy objects.

My code

I am getting the list of custom objects defined in one of my Apex classes by calling Apex method from LWC JS file:

getSettingsForConfigType({configType: this.codeConfigType})
            .then(settings => {
                //this.fieldList = settings;
                this.prepopulateConfig(settings);
            })
            .catch(error => {
                this.toastError(error.body.message);
            })

The problem

The problem is I need to populate the settings object returned from Apex with additional field. This field is not defined in Apex (and I don't want it to be defined, it will be used only on LWC side). Whenever I try to add new field called fieldValue either with obj.fieldValue = ... or obj['fieldValue'] = ... syntax I get forrowing error:

TypeError: 'set' on proxy: trap returned falsish for property 'fieldValue'

Question

Is there any way to overcome this limitation or maybe I am missing something here?

P.S. Dirty workaround

settings = JSON.parse(JSON.stringify(settings));

However, it seems to be a bit ugly trick. That's why I posted the question :-)

Answer 1

Try using ES6 syntax, looks much cleaner and simpler.

const fieldValue = (whatever data to add)
settings = {...settings, fieldValue};