Gatsby Node API onPostBuild in gatsby-node.js 无法执行

Question

 module.exports = { parseXML: function(file_path, callback) { callback("test 1") readFile(file_path.toString(), "utf-8", function(err, data) { if (err) callback(err); parseString(data, function(err, result) { if (err) callback(err); callback("test 2") var json = result; delete json.sitemapindex.sitemap[1].lastmod; var builder = new xml2js.Builder(); var xml = builder.buildObject(json); write2File(file_path.toString(), xml, function(err, data) { if (err) callback(err); callback("test 3") callback("successfully written our update xml to ",file_path.toString()); }); }); }); callback("test 4") } }

This is a function to parse XML to JSON and modify the JSON and write back to XML. I called this function in gatsby-node.js in onPostBuild like this

exports.onPostBuild = async () => {sitemap_mod.parseXML("filename")}

However, in the gatsby build , it only printed out test:1 and test:4 , which means it failed to execute anything in the readFile function. I suppose this is because the onPostBuild is an async function and I need to add some await state in my code. I applied this function in other node API such as onPostBootstrap and onCreateDevServer and they were both working properly, able to execute readFile and write2File function. So I think there's something wrong about my usage of onPostBuild . Thanks for your help!

Answer 1

Yes, you should indeed make sure to wait for the function to finish.

You need to wait for the three asynchronous calls you have inside parseXML . I usually use promisify to turn them into async functions:

const { promisify } = require("util");
const asyncParseString = promisify(parseString);
const asyncReadFile = promisify(readFile);
const asyncWrite2File = promisify(write2File);

function transformJsonToXml(json) {
  ...
} 

async function parseXML(file_path) {
  const data = await asyncReadFile(file_path.toString(), "utf-8");
  const json = await asyncParseString(data);

  await asyncWrite2File(file_path.toString(), transformJsonToXml(json));
}

Your onPostBuild then needs to wait for parseXML to finish. So either put an await before the parseXML call or just use

exports.onPostBuild = () => sitemap_mod.parseXML("filename")