How do i store an object value in an array in JavaScript?

Question

When i try to store an object value within an array it says the content is undefined, although i'm not sure why it is so. Whenever i call the object through console.log it properly shows itself. How can i do that?

myHeaders = new Headers({
    "git-user": "git-user",
    "response": "JSON"
});
var myHeader = {
    method: 'GET',
    headers: myHeaders,
};
var array_nome = new Array();
var Johnson, Johnson1;
var api_url = "url";
fetch(api_url, myHeader)
    .then(response => Johnson = response.json())
    .then(data => Johnson1 = data)
Johnson1 = JSON.stringify(Johnson1);
let selection_array = new Array();
for (let i = 0; i < 32; i++) {
    array_name[i] = Johnson1.Result[i].Name
}