How to get data from this ajax call

Hi guys,
I retrieved data from server with the ajax method but I don't know how to extract this data out of response text to use it somewhere else.
Any suggestions how to do this would be greatly appreciated.

fetch("/path_to_file/data.json").then(response => {
    return response.text();
}).then(data => {
    if(data) {
        var foo = JSON.parse(data);
        console.log(data); // {"key1":"value1","key2":"value2"}
        retrieveData(foo.key1,foo.key2);
    }
});
function...

Code (markup):

How to get data from this ajax call

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