为什么 fs.writeFileSync() 会抛出“不是函数”错误？

Question

I am trying to save some data in a file using fs.writeFileSync, but it doesn't work and I cannot figure out why. It throws the following error: Unhandled Rejection (TypeError): fs.writeFileSync is not a function

In my app I use it like this:

const fs = require('fs');
const stateFile = "./usersStateFile";

const saveLastEventSequenceId = (sequenceId) => {
    try {
            fs.writeFileSync(stateFile, sequenceId);
        } catch (err) {
          throw err;
        }
     };

The sequenceId is a number and the ./usersStateFile doesn't exist, but fs.writeFileSync() should create it if it doesn't exist.

What might be the problem?

Answer 1

Import fs module like so:

const fs = require('fs'); // or `import * as fs from 'fs'` if you're using ES2015+
const stateFile = "./usersStateFile";

const saveLastEventSequenceId = (sequenceId) => {
  try {
    fs.writeFileSync(stateFile, sequenceId);
  } catch (err) {
    throw err;
  }
};

You were calling fs.writeFileSync() without having a variable named fs that's defined in your scope. In this case, fs evaluates to undefined , which caused the error when trying to invoke its in-existent function member.