使用 readline 的异步标准输入

Question

我正在查看 O'Reilly 书中的一个示例“JavaScript：权威指南”，并试图进行一些更改。

当您使用输入重定向时，这个例子在书中写得很好：

node charfreq.js < input.txt

但我想进行更改，以便用户可以通过 Win cmd 行输入行，完成后 (ctrl+D)，让脚本继续。为此，我尝试使用 readline 而不是 process.stdin，但无法让 asyn 工作。

这是原始代码：

async function histogramFromStdin() {
    process.stdin.setEncoding("utf-8"); // Read Unicode strings, not bytes
    let histogram = new Histogram();
    for await (let chunk of process.stdin) {
        histogram.add(chunk);
    }

    return histogram;
}

// This one final line of code is the main body of the program.
// It makes a Histogram object from standard input, then prints the histogram.
histogramFromStdin().then(histogram => { console.log(histogram.toString()); });

到目前为止，这是我尝试过的：

这里的问题是对 console.log(histogram.toString()); 的调用立即发生，而直方图仍未定义。不确定在哪里等待。

async function histogramFromStdin() {
    var readline = require('readline');
    process.stdin.setEncoding('utf-8');
    let histogram = new Histogram();

    var rl = readline.createInterface({ input: process.stdin, output: process.stdout });
    rl.setPrompt('> ');
    rl.prompt();
    rl.on('line', function (chunk) { histogram.add(chunk); rl.prompt(); });
    rl.on('close', function () { console.log('Input has closed'); return histogram; });
}

// This one final line of code is the main body of the program.
// It makes a Histogram object from standard input, then prints the histogram.
histogramFromStdin().then(histogram => { console.log(histogram.toString()); });

Answer 1

您可以根据文档使用async/await 和events 的混合方法：Example: Read file stream line-by-Line: a mixed approach

尝试这个：

const readline = require('readline');
const {once} = require('events');

async function histogramFromStdin() {

    process.stdin.setEncoding('utf-8');
    let histogram = new Histogram();
  
    try {
        
        const rl = readline.createInterface({ input: process.stdin, output: process.stdout });

        rl.setPrompt('> ');
        rl.prompt();
        rl.on('line', function (chunk) { histogram.push(chunk); rl.prompt(); });

        await once(rl, 'close');

        console.log('Input has closed');

        return histogram;

    } catch (err) {

        console.error(err);
    }


}

// This one final line of code is the main body of the program.
// It makes a Histogram object from standard input, then prints the histogram.
histogramFromStdin().then(histogram => { console.log(histogram.toString()); })