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Am not doing anything fancy, just trying to update a field on Contact in JS of LWC but getting this exception.

Uncaught TypeError: 'set' on proxy: trap returned falsish for property 'Name'
throws at mydomain/auraFW/javascript/mhontaYdOya4Y_lBu7v9yg/aura_prod.js:2:27687

HTML Code:

<template>

 <template if:true=wiredContact>

 wiredContact.Name

 <lightning-input value=wiredContact.Name onchange=updateName></lightning-input>
 </template>

</template>

JS:

import LightningElement ,wire,track,api from 'lwc';
import myContact from "@salesforce/apex/ContactController.fetchContact";

export default class Myrefreshapextest extends LightningElement 


 @track wiredContact;

 @wire (myContact)
 fetchedContact(error, data)
 if(data)
 console.log(JSON.stringify(data));
 this.wiredContact = data;
 else if (error)
 console.log(error);
 
 

 updateName (event)
 console.log(JSON.stringify(event.detail.value));
 console.log(JSON.stringify(this.wiredContact));
 this.wiredContact.Name = event.detail.value;
 

Apex:

public class ContactController 

 @AuraEnabled(cacheable=true)
 public static Contact fetchContact()
 return [SELECT Id,Name FROM COntact LIMIT 1];
 

On top of my head, am not doing anything wrong, anyone has idea what's wrong with my code?

When I print console.log(JSON.stringify(this.wiredContact)); I get old values so am pretty sure it exists.

I tried with @track and @api, but same response. Can anyone shed some light?

Cached items are set as read-only (because otherwise you could corrupt the cache). If you want a modifiable object, you need to clone it.

this.wiredContact = Object.assign(, data);

This is what I could find from the documentation for wired service and that seems to be the case here (emphasis mine).

The wire service provisions an immutable stream of data to the component

So it most likely seems that when trying to set the values directly using this.wiredContact.Name, because of it's read only property, the values are not getting set.

However if you try to create a new data and then assign it to this.wiredContact, it works:

this.wiredContact = "Name:" + event.detail.value + "";