我正在从API中提取一个Excel文件,需要使用xlsx库读取和修改它。我正在使用节点 8.10 并为此异步/等待:
const report = await getVisitorReport(visitorQueryString, 'test12.xls', uri);
let workbook = XLSX.readFile('test12.xls');
这是函数getVisitorReport。请注意,我解决了管道完成时的承诺:
async function getVisitorReport(queryString, reportPath, uri) {
return new Promise((resolve, reject) => {
request({
url: uri,
qs: queryString,
headers: {
'Content-Type': 'application/json',
'Accept': 'application/json',
'Authorization': 'Basic ' + new Buffer(process.env.username + ':' + process.env.password, 'utf8').toString('base64')
}
}, (error, response, body) => {
if (error) {
reject(error);
} else {
if (response.statusCode === 200) {
resolve(body);
} else if (response.statusCode === 409) {
setTimeout(() => {
resolve(getVisitorReport(queryString));
}, response.headers['Retry-After'] * 1000);
} else {
reject(response);
}
}
}).pipe(fs.createWriteStream(reportPath)).on('finish', resolve(reportPath));
});
}
文件已正确拉取和创建。似乎第二行XLSX.readFile('test12.xls'(发生在文件在本地保存之前。我在这里做错了什么?如何确保在尝试读取文件之前已保存文件?为什么 .pipe.on('finish', resolve( 没有完成此操作? 感谢您的帮助!
代码立即调用resolve
:.on('finish', resolve(reportPath))
。
您可以将解析函数直接提供给on
处理程序:
.on('finish', resolve)
或者,如果需要传递一些数据,请使用箭头函数:
.on('finish', () => resolve(args))
编辑:
如果你这样做:.on('finish', resolve(reportPath))
它大致等于
resolve(reportPath); // immediately calls resolve which makes a promise resolved
// so await doesn't stop the further code execution
....on('finish', undefined)
为了更好地理解,请看这个例子:
const [bad, good] = document.querySelectorAll("button");
bad.addEventListener("click", console.log("I log immediately when the page loads and not at click event"))
good.addEventListener("click", () => console.log("I log properly when button is clicked"))
<button>broken button</button>
<button>good button</button>