How to use variable in Wire method in Lightning Web Component

The wire service provisions an immutable stream of data to the component. Each value in the

 stream is a newer version of the value that precedes it.

We call the wire service reactive in part because it supports reactive variables, which

 are prefixed with $. If a reactive variable changes, the wire service provisions new data. 

Use '$variableName' while calling wire method instead of using this.variableName. 

This will avoid the undefined variable issue while calling Wire method in Salesforce.

Check the following sample code. '$recordId' will not throw any error. But, if this.recordIdis used, it will throw 

undefined exception. 

import { LightningElement, api, wire } from 'lwc';
import { getRecord } from 'lightning/uiRecordApi';

export default class Record extends LightningElement {
    @api recordId;

    @wire(getRecord, { recordId: '$recordId', fields: ['Account.Name'] })
    record;
}