NodeJS Plotly-如何在继续继续之前等待getImage完成 [英] NodeJS Plotly - how to wait for getImage to finish before continuing

问题描述

所以，我想要完成的基本上是:使用NodeJS生成一个图，并为NodeJS绘制图，然后将其放入我的文件系统中(使用 getImage )，然后进行图像处理.我的问题是，该函数在完成并将图像放入文件系统之前会返回.因此，我的结果基本上是，在调用 generate_plot()之后，该文件尚不存在，并且出现了错误.现在，我的问题是:我如何等待 generate_plot()完成并将图像放入文件系统，然后继续使用该图像/使用该图像?

So, what I am trying to accomplish is basically: Generating a plot by using NodeJS and plotly for NodeJS and getting it into my filesystem (with getImage), and proceeding with the image afterwards. My problem is, that the function returns before finishing and getting the image into my filesystem. So my result is basically that after I'm calling generate_plot(), the file does not exist yet and I'm getting an error. Now onto my question: How do I wait for generate_plot() to finish and to getting the image into my filesystem before continuing and using this image/to use this image?

const fs = require("fs");
var plotly = require('plotly')(username, api_key);

function generate_plot(){
    var trace = {
      type: 'bar',
      x: ['Mario', 'Luigi', 'Bowser'],
      y: [50000, 10000, 2000],
      marker: {color: ["red", "green", "darkblue"]},
    };

    var layout = {
      plot_bgcolor: 'rgb(52, 54, 60)',
      paper_bgcolor: 'rgb(52, 54, 60)',
    };

    var chart = {data: [trace], layout: layout};

    var pngOptions = {format: 'png', width: 1000, height: 500};

    plotly.getImage(chart, pngOptions, function (err, imageData) {
        if (err) throw err
        var pngStream = fs.createWriteStream('test.png');
        imageData.pipe(pngStream);
    })
}

function run(){
    generate_plot()
    // proceed with the generated plot which should be in the filesystem
}

推荐答案

欢迎使用堆栈溢出！

我删除了之前的答案，因为(正如您正确指出的那样)它们不能解决全部问题.

I have removed my previous answers, because (as you correctly pointed out) they didn't solve the full problem.

在返回 generate_plot()函数之外的控制之前，需要完成两个异步任务:从Plotly检索数据，并将该内容写入磁盘.

There are two asynchronous tasks that need to complete before we return control outside of the generate_plot() function: retrieving data from Plotly, and writing that content to disk.

下面的示例调用 generate_plot()，然后(作为验证文件是否确实在磁盘上的测试)，它将立即将 test.png 复制到 test2.png .因为这导致两个文件的大小相同，所以这表明 fs.copyFileSync 在 test.png 文件完全位于磁盘上之前不会运行.

The example below calls generate_plot(), and then (as a test to validate whether the file is really on disk) it immediately copies test.png to test2.png. Because this results in both files being the same size, this demonstrates that the fs.copyFileSync is not running until the test.png file is fully on disk.

我确实稍微更改了一些变量名，但这应该可以正常工作.

I did change some of your variable names slightly, but this should work now.

为等待文件流完成，请参考以下问题:与node.js中的fs.createWriteStream关联的事件

For waiting for the file stream to finish, I reference this question: event associated with fs.createWriteStream in node.js

function generate_plot() {
  return new Promise((resolve, reject) => {
    var trace = {
      type: 'bar',
      x: ['Mario', 'Luigi', 'Bowser'],
      y: [50000, 10000, 2000],
      marker: { color: ["red", "green", "darkblue"] },
    };

    var layout = {
      plot_bgcolor: 'rgb(52, 54, 60)',
      paper_bgcolor: 'rgb(52, 54, 60)',
    };

    var chart = { data: [trace], layout: layout };

    var pngOptions = { format: 'png', width: 1000, height: 500 };

    plotly.getImage(chart, pngOptions, (err, imageStream) => {
      if ( err ) return reject(err);
      var fileStream = fs.createWriteStream('test.png');
      imageStream.pipe(fileStream);
      fileStream.on('error', reject);
      fileStream.on('finish', resolve);
    });
  });
}

function run() {
  generate_plot()
    .then(() => {
      fs.copyFileSync('test.png', 'test2.png');
      console.log('done');
    })
    .catch(err => {
      console.log(err);
    });
}

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