Question

请有人可以帮助我吗？我的问题是：为什么我不能在jason.js中异步编写然后同步读取它？

为使我的问题更清楚，这是我的代码：

const fs = require('fs');

var originalNote = {
   title: 'todo list',
   body : `that's my secret`
};

var stringNote = JSON.stringify(originalNote);

//here I write asynchronously into my note.json file
fs.writeFile('note.json',stringNote, () => {
       console.log('hey there');
});

//here I read synchronously from the note.json file
var file = fs.readFileSync('./note.json');
var note = JSON.parse(file);

执行此操作时，出现以下错误：

SyntaxError: Unexpected end of JSON input

at JSON.parse (<anonymous>)

at Object.<anonymous> (/Users/yosra/Desktop/notes-node/playground/json.js:31:18)

at Module._compile (internal/modules/cjs/loader.js:721:30)

at Object.Module._extensions..js (internal/modules/cjs/loader.js:732:10)

at Module.load (internal/modules/cjs/loader.js:620:32)

at tryModuleLoad (internal/modules/cjs/loader.js:560:12)

at Function.Module._load (internal/modules/cjs/loader.js:552:3)

at Function.Module.runMain (internal/modules/cjs/loader.js:774:12)

at executeUserCode (internal/bootstrap/node.js:342:17)

at startExecution (internal/bootstrap/node.js:276:5)

但是当我使所有内容同步时，它就会起作用。

非常感谢

Answer 1

您要尝试在文件写入后读取。这意味着您必须在writeFile的回调函数中执行此操作。

//here I write asynchronously into my note.json file
fs.writeFile('note.json',stringNote, () => {
    console.log('hey there');
    //here I read synchronously from the note.json file
    var file = fs.readFileSync('./note.json');
    var note = JSON.parse(file);

});

Answer 2

欢迎堆栈溢出！

关于您的问题，您没有正确处理异步代码。您的读应该在写后发生，所以您应该执行以下操作：

const fs = require('fs');

var originalNote = {
   title: 'todo list',
   body : `that's my secret`
};

var stringNote = JSON.stringify(originalNote);

//here I write asynchronously into my note.json file
fs.writeFile('note.json',stringNote, () => {
       console.log('hey there');
       //here I read synchronously from the note.json file
       var file = fs.readFileSync('./note.json');
       var note = JSON.parse(file);
});

节点js：为什么我不能在jason.js中异步编写然后同步读取它？

2 个答案: