Node.js代码运行时输出多余行问题修复求助

问题场景 #

执行命令node index.js test.txt '${1} ${2} ${3} ${4}'时，预期输出文件每行的前4个单词，但实际输出多了一行 ${2} ${3} ${4}。

原代码如下：

const fs = require('fs');

function processFile(filePath) {
  const content = fs.readFileSync(filePath, 'utf-8');
  const lines = content.split('\n');

  const wordIdMaps = lines.map(() => ({ wordIdMap: {}, currentId: 1 }));

  lines.forEach((line, index) => {
    const words = line.split(' ');
    const wordIdMap = wordIdMaps[index].wordIdMap;
    let currentId = wordIdMaps[index].currentId;

    words.forEach((word) => {
      if (!wordIdMap[word]) {
        wordIdMap[word] = currentId;
        currentId++;
      }
    });
  });

  return { lines, wordIdMaps }; // Return both lines and wordIdMaps
}

function customConsoleLog(logFormat, wordIdMaps) {
  const lines = wordIdMaps.map((map) => Object.entries(map.wordIdMap).map(([word, id]) => `${word}:${id}`).join(' '));

  lines.forEach((line, index) => {
    const wordIdMap = wordIdMaps[index].wordIdMap;

    const replacedLog = logFormat.replace(/\${(\d+)}/g, (_, id) => {
      const word = Object.keys(wordIdMap).find((key) => wordIdMap[key] == id);
      return word !== undefined ? word : '${' + id + '}';
    });

    const words = line.split(' ');
    const replacedLine = replacedLog.replace(/\${\d+}/g, (match) => {
      const id = match.slice(2, -1);
      return words[id - 1] !== undefined ? words[id - 1] : match;
    });

    console.log(replacedLine);
  });
}

// Command-line arguments
const filePath = process.argv[2];
const logFormat = process.argv[3];

if (!filePath || !logFormat) {
  console.log('Please provide both a file path and a custom console log format as command-line arguments.');
} else {
  const { lines, wordIdMaps } = processFile(filePath);

  customConsoleLog(logFormat, wordIdMaps);
}

预期输出：

apple boy cat dog
elephant fish god hen

实际输出：

apple boy cat dog
elephant fish god hen
 ${2} ${3} ${4}

错误原因 #

问题出在processFile函数的content.split('\n')：当文本文件末尾存在换行符时，拆分后会生成一个空字符串元素。这个空行对应的wordIdMap是空对象，在customConsoleLog处理时，无法找到对应单词替换${1}，导致${1}被替换为空，剩下 ${2} ${3} ${4}输出，形成多余行。

修复方案 #

步骤1：过滤空行 #

在processFile函数中，拆分行后过滤掉空行和纯空白行：
将

const lines = content.split('\n');

修改为

const lines = content.split('\n').filter(line => line.trim() !== '');

步骤2：优化customConsoleLog函数（可选） #

原函数存在冗余的行生成逻辑，且两次替换属于重复操作，可简化为一次替换：

function customConsoleLog(logFormat, lines) {
  lines.forEach(line => {
    const words = line.split(' ');
    const replacedLine = logFormat.replace(/\${(\d+)}/g, (_, id) => {
      const idx = parseInt(id) - 1;
      return words[idx] !== undefined ? words[idx] : `\${${id}}`;
    });
    console.log(replacedLine);
  });
}

调用时只需传入lines：

customConsoleLog(logFormat, lines);

修复后的完整代码 #

const fs = require('fs');

function processFile(filePath) {
  const content = fs.readFileSync(filePath, 'utf-8');
  // 过滤空行和纯空白行
  const lines = content.split('\n').filter(line => line.trim() !== '');

  const wordIdMaps = lines.map(() => ({ wordIdMap: {}, currentId: 1 }));

  lines.forEach((line, index) => {
    const words = line.split(' ');
    const wordIdMap = wordIdMaps[index].wordIdMap;
    let currentId = wordIdMaps[index].currentId;

    words.forEach((word) => {
      if (!wordIdMap[word]) {
        wordIdMap[word] = currentId;
        currentId++;
      }
    });
  });

  return { lines, wordIdMaps };
}

function customConsoleLog(logFormat, lines) {
  lines.forEach(line => {
    const words = line.split(' ');
    const replacedLine = logFormat.replace(/\${(\d+)}/g, (_, id) => {
      const idx = parseInt(id) - 1;
      return words[idx] !== undefined ? words[idx] : `\${${id}}`;
    });
    console.log(replacedLine);
  });
}

// Command-line arguments
const filePath = process.argv[2];
const logFormat = process.argv[3];

if (!filePath || !logFormat) {
  console.log('Please provide both a file path and a custom console log format as command-line arguments.');
} else {
  const { lines } = processFile(filePath);
  customConsoleLog(logFormat, lines);
}

验证效果 #

执行原命令后，输出将与预期一致，不会出现多余的空行及未替换的占位符。

内容的提问来源于stack exchange，提问作者coco bar