Download Progress Tool in Terminal Using Node.JS

June 7, 2019

TL;DR:

fs.stat for getting file size
readline.clearLine
readline.cursorTo(0)
process.stdout.write

Combine these 3 to update command line instead of printing new line

Get file size

fs.stat returns an object contains several stats of the file from url you're downloading.

Inside of the object, there is size property, which is obviously the size of file, in bytes.

let fileSize = 0;
fs.stat("url/to/your/file", (stats) => {
  fileSize = stats.size;
});

Get current progression

In the response from https.get when downloading, track and add up the total length of chunks piped into fs.writeStream. This total length devided by file size is the download progression we need.

Write to terminal, but in same line

console.log implementation in Node is actually based on process.stdout.write. But since there's a \\n at end of every console.log, new line is printed everytime instead of being updated. Therefore we can't use console.log

By combine readline.clearLine and readline.cursorTo(0), terminal will erase the last line of currently printed line, then move cursor to the starting position. Then we can use process.stdout.write to print out current progress without \\n in console.log implementation that causes changing line.

let progress = 0;
let req = https.get("url/to/your/file", (res, err) => {
  res.on("data", (chunk) => {
    progress += chunk.length;
    const dlPercentage = ((progress / fileSize) * 100).toFixed(2);
    readline.clearLine();
    readline.cursorTo(0);
    process.stdout.write(`Downloading... ${dlPercentage}%`);
  });
});