diff --git a/build/jsconfig.json b/build/jsconfig.json
index a731bfcdfce512bade028325a5999a64572393c6..299294ef05588f6619a99ff5f9f72fda5ee9dc59 100644
--- a/build/jsconfig.json
+++ b/build/jsconfig.json
@@ -2,7 +2,8 @@
 	"compilerOptions": {
 		"module": "commonjs",
 		"target": "es2017",
-		"jsx": "preserve"
+		"jsx": "preserve",
+		"checkJs": true
 	},
 	"include": [
 		"**/*.js"
diff --git a/build/npm/postinstall.js b/build/npm/postinstall.js
index 2aaa93528f5228ae6eb245000cc43918f5a08cd8..6df0b4ecb23a268c7ea5eb80928879a874f885bc 100644
--- a/build/npm/postinstall.js
+++ b/build/npm/postinstall.js
@@ -8,6 +8,10 @@ const path = require('path');
 const fs = require('fs');
 const yarn = process.platform === 'win32' ? 'yarn.cmd' : 'yarn';
 
+/**
+ * @param {string} location
+ * @param {*} [opts]
+ */
 function yarnInstall(location, opts) {
 	opts = opts || {};
 	opts.cwd = location;
diff --git a/build/npm/update-all-grammars.js b/build/npm/update-all-grammars.js
index af2db363e6a0607a4e723f8fd0aa2dbf75e4b24e..3ff7254c3e2825c2283fd6f720830ca3a16a8f2b 100644
--- a/build/npm/update-all-grammars.js
+++ b/build/npm/update-all-grammars.js
@@ -7,6 +7,9 @@ const cp = require('child_process');
 const fs = require('fs');
 const path = require('path');
 
+/**
+ * @param {string} location
+ */
 function updateGrammar(location) {
 	const npm = process.platform === 'win32' ? 'npm.cmd' : 'npm';
 	const result = cp.spawnSync(npm, ['run', 'update-grammar'], {
diff --git a/build/npm/update-grammar.js b/build/npm/update-grammar.js
index 988b7bc3795ccf7093d0c047c0d3aa2bcea14573..2ccd808e152bf0f0889d1f4e3ed9d70cc2480b9f 100644
--- a/build/npm/update-grammar.js
+++ b/build/npm/update-grammar.js
@@ -12,6 +12,9 @@ var cson = require('cson-parser');
 var https = require('https');
 var url = require('url');
 
+/**
+ * @param {string} urlString
+ */
 function getOptions(urlString) {
 	var _url = url.parse(urlString);
 	var headers = {
@@ -19,7 +22,7 @@ function getOptions(urlString) {
 	};
 	var token = process.env['GITHUB_TOKEN'];
 	if (token) {
-		headers['Authorization'] = 'token ' + token
+		headers['Authorization'] = 'token ' + token;
 	}
 	return {
 		protocol: _url.protocol,
@@ -30,6 +33,10 @@ function getOptions(urlString) {
 	};
 }
 
+/**
+ * @param {string} url
+ * @param {number} redirectCount
+ */
 function download(url, redirectCount) {
 	return new Promise((c, e) => {
 		var content = '';