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feat: Leading and trailing edge debounce for the file watch #9

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feat: Leading and trailing edge debounce for the file watch #9

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75 changes: 57 additions & 18 deletions lib/dev-middleware.js
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Original file line number Diff line number Diff line change
Expand Up @@ -3,6 +3,7 @@ let chokidar = require('chokidar');
let expressws = require('express-ws');
let fs = require('fs');
let url = require('url');
let crypto = require('crypto');

const MIME_TYPES = {
'mjs': 'application/javascript',
Expand All @@ -13,6 +14,7 @@ const MIME_TYPES = {
module.exports = function (app, config, options) {
expressws(app);
let files = {};
const fileHashes = {};
let sockets = [];

if (options.hot) {
Expand Down Expand Up @@ -105,28 +107,65 @@ module.exports = function (app, config, options) {
console.log('\x1b[32m%s\x1b[0m', `Compiled in ${response.stats.time}ms.`);
}

async function compiler () {
let bundle = await nollup(config);
let watcher = chokidar.watch(options.watch);
let watcherTimeout;
function debounceLeadingAndTrailing(func, wait) {
let timeout;
let needsCalling = false;

return function executedFunction() {
let context = this;
let args = arguments;

let later = function() {
timeout = null;
if (needsCalling) {
func.apply(context, args)
needsCalling = false;
};
};

let callNow = !timeout;

clearTimeout(timeout);

timeout = setTimeout(later, wait);

if (callNow) {
func.apply(context, args)
} else {
needsCalling = true;
}
};
};

const onChange = async (path) => {
if (fs.lstatSync(path).isFile()) {
files = {};
bundle.invalidate(path);
const onChange = async (path, bundle) => {
if (fs.lstatSync(path).isFile()) {
// read out the file and generate a hash
const file = fs.readFileSync(path);
const hash = crypto.createHash('md5').update(file).digest("hex");

// if the hash is the same as it was last time, bail and don't recompile
if (fileHashes[path] === hash) {
return
}

if (watcherTimeout) {
clearTimeout(watcherTimeout);
}
// set the hash so that next time we can bail early
fileHashes[path] = hash;

files = {};
bundle.invalidate(path);

watcherTimeout = setTimeout(async () => {
handleGeneratedBundle(await bundle.generate());
}, 100);
}
};
handleGeneratedBundle(await bundle.generate());
}
};

async function compiler () {
let bundle = await nollup(config);
let watcher = chokidar.watch(options.watch, { ignoreInitial: true });

const debouncedOnChange = debounceLeadingAndTrailing(path => onChange(path, bundle), 300);

watcher.on('add', onChange);
watcher.on('change', onChange);
watcher.on('add', debouncedOnChange);
watcher.on('change', debouncedOnChange);

handleGeneratedBundle(await bundle.generate());
};
Expand Down