Safe Assignment Operator in JavaScript, a myth or reality?

I’ve been going through Medium to get some updates about programming. A couple of articles confused me that were related to “Safe Assignment Operator”:

async function getData() {
    const [networkError, res] ?= await fetch('https://api.backend.com/resource/1')
    
    if(networkError) console.error(networkError)
    const [parseError, data] ?= await res.json()

    if(parseError) console.error(parseError)
    return data
            
}

I tried finding the official documentation on MDN, but nothing found. I also tried on console but no luck.

Is this a myth or isn’t the MDN site updated?