Node.js使用line-by-line依赖时readline输入提示无响应问题

问题根因 #

你代码的问题出在readline模块的question方法是异步执行的：

• 调用rl.question()时只会先把问题打印出来，传入的回调函数要等用户实际输入内容按下回车之后才会执行
• 你当前的代码顺序执行时，三个rl.question触发打印后，主线程会立刻执行后面的拼接打印逻辑，此时三个变量还没被回调赋值，所以全是undefined
• 打印完你又直接调用了rl.close()关闭了输入接口，程序直接终止，根本不会等待用户输入

修复方案 #

方案1：回调嵌套（最直观的适配写法） #

把后续的提问逻辑和收尾操作都放在前一个提问的回调里，保证顺序执行：

var rlname;
var rlage;
var rlcolor;

const readline = require('readline');
const rl = readline.createInterface ({
    input: process.stdin,
    output: process.stdout,
    prompt: '>'
});

function getUserInput() {
    rl.question("What is your name? \n", (name) => {
        rlname = name;
        rl.question("What is your age? \n", (age) => {
            rlage = age;
            rl.question("What is your favorite color? \n", (color) => {
                rlcolor = color;
                console.log("Hello " + rlname + ", you are " + rlage + " years old and your favorite color is " + rlcolor + ".");
                // 所有逻辑执行完再关闭接口
                rl.close();
            })
        })
    })
}

getUserInput();

方案2：Promise+async/await（代码结构更清晰，避免回调嵌套） #

把提问逻辑封装成Promise，用同步的写法实现异步执行顺序：

const readline = require('readline');
const rl = readline.createInterface ({
    input: process.stdin,
    output: process.stdout,
    prompt: '>'
});

// 封装提问为Promise
function question(query) {
    return new Promise(resolve => rl.question(query, resolve));
}

async function getUserInput() {
    const rlname = await question("What is your name? \n");
    const rlage = await question("What is your age? \n");
    const rlcolor = await question("What is your favorite color? \n");
    console.log(`Hello ${rlname}, you are ${rlage} years old and your favorite color is ${rlcolor}.`);
    rl.close();
}

getUserInput();

内容的提问来源于stack exchange，提问作者Fikrys