想问，怎么把callback函数的内容拿出来。。
const fs = require('fs')
var text
fs.readFile('./test.txt', {encoding:''}, function(err, data){
if(err){
console.log(err);
}else{
text = data.toString()
console.log(data.toString());
}
});
console.log('This is the end.')
console.log('out:',text)
输出
This is the end.
out: undefined
This is a test file.
怎么让那个out等到text被赋值了再输出啊
14 回复
const fs = require('fs')
var text
function getText(){
return new Promise((resolve,reject)=>{
fs.readFile('./test.txt', {encoding:''}, function(err, data){
if(err){
reject(err)
}else{
text = data.toString()
resolve(text)
}
});
})
}
(async (){
let text = await getText()
console.log('This is the end.')
console.log('out:',text)
})()
现在 fs 标准库已经支持 Promise 了 https://nodejs.org/dist/latest-v14.x/docs/api/fs.html#fs_promise_example：
const fs = require('fs/promises');
(async function(path) {
try {
await fs.unlink(path);
console.log(`successfully deleted ${path}`);
} catch (error) {
console.error('there was an error:', error.message);
}
})('/tmp/hello');
