fetch请求函数封装思路

requestFetch(url, data = {}, method = 'POST', formData = false) {
    return new Promise((resolve, reject) => {
        let form_data = formData ? data : JSON.stringify(data);
        fetch(url, {method,
            headers: {
                    'Content-Type': formData ? 'application/x-www-form-urlencoded':'application/json',},
            body: form_data
        })
        .then((res) => {
            return res.json();
        })
        .then((res) => {
            resolve(res)
        }).catch(err => {
            reject(err)
        });
    });
}