Set up dev environment

.eslintrc.json

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+{
+    "root": true,
+    "env": {
+        "node": true,
+        "es2021": true
+    },
+    "plugins": [
+    ],
+    "extends": [
+        "eslint:recommended"
+    ],
+    "parserOptions": {
+        "ecmaVersion": "latest",
+        "sourceType": "module"
+    },
+    "rules": {
+        "no-prototype-builtins": 0,
+        "no-var": 1,
+        "no-trailing-spaces": 1
+    },
+    "overrides": [
+        {
+            "files": [ "*.spec.js" ],
+
+            "env": { "mocha": true },
+            "plugins": [
+                "mocha",
+                "chai-expect"
+            ],
+            "rules": {
+                "mocha/no-sibling-hooks": "off",
+                "mocha/max-top-level-suites": "off"
+            },
+           "extends": [
+                "plugin:mocha/recommended",
+                "plugin:chai-expect/recommended"
+            ],
+            "globals": {
+                "describe": "readonly",
+                "context": "readonly",
+                "before": "readonly",
+                "beforeEach": "readonly",
+                "after": "readonly",
+                "afterEach": "readonly",
+                "it": "readonly",
+                "expect": "readonly"
+            }
+        },
+        {
+            "files": [ "*.peg" ],
+
+            "plugins": [ "@peggyjs" ],
+            "extends": ["plugin:@peggyjs/recommended"]
+        }
+
+    ]
+}

.mocharc.cjs

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+module.exports = {
+	extension: '.spec.js',
+	loader: 'esmock',
+	colors: true,
+	require: 'mocha.conf.js'
+}

gulpfile.js

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+import gulp from 'gulp';
+import tap from 'gulp-tap';
+import rename from 'gulp-rename';
+import peggy from 'peggy';
+
+const buildParser = function() {
+	return gulp.src('selector.peg')
+		.pipe(tap(function(file) {
+			file.contents = new Buffer(peggy.generate(file.contents.toString('utf-8'), {
+				output: 'source',
+				format: 'es'
+			}));
+		}))
+		.pipe(rename(function(path) {
+			path.extname = '.js';
+		}))
+		.pipe(gulp.dest('.'));
+}
+buildParser.displayName = 'build-parser';
+
+gulp.task(buildParser);
+gulp.task(function watch() {
+	gulp.watch(['*.peg'], { usePolling: process.env.GULP_WATCH_POLLING }, buildParser);
+});

mocha.conf.js

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+import chai from 'chai';
+import sinonChai from 'sinon-chai';
+
+global.expect = chai.expect;
+chai.use(sinonChai);