// test.txt  -->  adsasdsa55
axios.get('./test.txt', { responseType: 'json' }).then(response => {
    console.log( response.data );
    // output `null`, illegal, awesome!
});

// test.json  -->  [1233]
axios.get('./test.json', { responseType: 'json' }).then(response => {
    console.log( response.data );
    // output Array(1233), ok!
});

// test.txt  -->  [false,5]
axios.get('./test.txt', { responseType: 'text' }).then(response => {
    console.log( typeof response.data );
    // output `object` , not `string`, why?
    console.log( response.data );
    // output Array(false, 5), not "[false,5]"
});