javascript - 使用 "fs"读取 JSON 文件会抛出 "invalid json"Node.js

Question

这让我抓狂。我不知道为什么，但是当我使用文件系统 require('fs') 读取有效的 Json 文件时，出现错误:无效的 json。这是代码:

var fs = require('fs');
const FILE_NAME = './json.json'

/*
// This way it works!
var jsonData = require('./json.json')
console.log(jsonData);
*/

async function readFile(filePath){
    return new Promise(function(resolve, reject){
        fs.readFile(filePath, 'utf8', function(err, contents) {
            if(err){
              console.log("Cant read the file " + err);
              reject(err)
            }
            else{
              resolve(contents)
            }
        })
    })
}

async function getNames(fileName){
  readFile(fileName).then(function(data){
    try {
      console.log(`Type of data: ` + typeof data);
      console.log("File data: " + data);
      return JSON.parse(data);
    } catch (error) {
      throw new Error( "Invalid JSON: " + error);
    }
  }).then(function(data){
    console.log(`FILE OBJECT: ` + data);
  }).catch(function(err){
    console.error(err);
  })
}
getNames(FILE_NAME)

这是文件内容:

{
  "name": "riko"
}

这是控制台输出:

Type of data: string
File data: {
  "name": "riko"
}
Error: Invalid JSON: SyntaxError: Unexpected token  in JSON at position 0
    at C:\Users\rojer\Desktop\Node\test\main.js:31:13

我知道我可以使用var jsonData = require('./json.json')，但是

1. 我想知道它不起作用的原因。
2. 如果 JSON 数据嵌入到常规文本文件中的某个位置会怎样？

好像有一些垃圾。

请帮忙。

Answer 1

这个:

Error: Invalid JSON: SyntaxError: Unexpected token  in JSON at position 0
    at C:\Users\rojer\Desktop\Node\test\main.js:31:13

tells us that there's an invisible character at the beginning of the file, probably a byte order mark (BOM), that require is handling but your code isn't. If the file is really in UTF-8, that BOM will be \xEF\xBB\xBF. Once read as UTF-8 into a JavaScript string, that will be the code point \u{FEFF} (because JavaScript strings are UTF-16 [but tolerate invalid surrogate pairs]). Update: Your binary listing of it confirms that.

I can confirm that if I have a UTF-8 JSON file with a BOM, require reads it and handles the BOM, but readFile returns the contents of the with the BOM intact, which trips up JSON.parse.

You can check for the BOM and strip it off, see *** lines:

const UTF8_BOM = "\u{FEFF}";                      // ***
async function getNames(fileName){
  readFile(fileName).then(function(data){
    try {
      console.log(`Type of data: ` + typeof data);
      if (data.startsWith(UTF8_BOM)) {            // ***
          data = data.substring(UTF8_BOM.length); // ***
      }
      console.log("File data: " + data);
      return JSON.parse(data);
    } catch (error) {
      throw new Error( "Invalid JSON: " + error);
    }
  }).then(function(data){
    console.log(`FILE OBJECT: ` + data);
  }).catch(function(err){
    console.error(err);
  })
}

---

或者，如果您不希望其中有 BOM，这里有一个快速但肮脏的工具，用于在 UTF-8 文件上添加/删除 BOM:

const fs = require("fs");

const UTF8_BOM = "\u{FEFF}";

const actions = new Map([
    ["-a", addBOM],
    ["-r", removeBOM],
    ["-t", toggleBOM]
]);

main();

function main() {
    const filename = process.argv[2];
    const option = process.argv[3] || "-t";
    const action = actions.get(option);

    if (!filename) {
        help();
        return;
    }

    if (!action) {
        console.error(`Invalid option ${option}`);
        help();
        return;
    }

    fs.readFile(filename, 'utf-8', (err, data) => {
        if (err) {
            console.error(`${filename}: Error reading file: ${err}`);
            return;
        }
        const hasBOM = data.startsWith(UTF8_BOM);
        action(filename, data, hasBOM);
    });
}

function writeResult(filename, data, toggle, successMessage, failMessage) {
    fs.writeFile(filename, data, "utf-8", (err) => {
        if (err) {
            console.error(`${filename}: ${failMessage}: ${err}`);
        } else {
            console.log(`${filename}: ${successMessage}${toggle ? " (toggled)" : ""}`);
        }
    });
}

function addBOM(filename, data, hasBOM, toggle) {
    if (hasBOM) {
        console.log(`${filename}: Already has a BOM`);
    } else {
        writeResult(filename, UTF8_BOM + data, toggle, "Added BOM", "Error adding BOM");
    }
}

function removeBOM(filename, data, hasBOM, toggle) {
    if (!hasBOM) {
        console.log(`${filename}: Already doesn't have a BOM`);
    } else {
        writeResult(filename, data.substring(UTF8_BOM.length), toggle, "Removed BOM", "Error removing BOM");
    }
}

function toggleBOM(filename, data, hasBOM) {
    if (hasBOM) {
        removeBOM(filename, data, hasBOM, true);
    } else {
        addBOM(filename, data, hasBOM, true);
    }
}

function help() {
    console.log("Usage: node utf8bomtoggle [filename] {options}");
    console.log("{options} can be:");
    console.log("  -t   Toggle a BOM [default]");
    console.log("  -a   Add a BOM if not present");
    console.log("  -r   Remove a BOM if present");
}