store JSON data from Fetch in a variable outside scope of fetch

Question

Hope all is well. Using node w fetch & trying to 'Get' the contents of a JSON file to be used in other functions in my script & possibly other scripts. Until now, i can only use them inside the fetch scope which is not optimal. pretty new to this but been workin on it for a couple days, read/watched a ton of tutorials, & searched here as well w no luck:-( for instance i'd like to do something like:

fetch (json){ }

let thePrice = data.price;

let theAmntSold = data.price;

....then later in script be able to use data.price & theAmntSold ie

totalAmntEarned(thePrice, theAmntSold) {
return thePrice * theAmntSold;
}

here is the latest I came up with and no luck

let theSystem, themaxPrice,
theblockPrices = [],
mainObj = {};

let showObj = function() {
//asyncronous so we need to set up for loop in a function
for (let prop in mainObj) {
    console.log(prop);
    console.log(mainObj[prop]);
}

};


fetch(URL, {
    method: 'GET',
    headers: {
        Authorization: AUTH_KEY
    }

}).then(function(resp) {
    return resp.json();
}) //assign variables below
.then(function(data) {
    showObj();
    let theblockPrices = data.blockPrices;
    
    console.log(data.maxPrice);
    console.log(theblockPrices[0]);
    });

so basically, i'd like to be able to use 'theblockPrices' in another function or variable. Also, when i call the showObj() inside the fetch block, I get no output in the console. Any tips would be amazing!

thanks