Initial commit: Developer Tools MVP with visual editor

- Complete React app with 7 developer tools
- JSON Tool with visual structured editor
- Serialize Tool with visual structured editor
- URL, Base64, CSV/JSON, Beautifier, Diff tools
- Responsive navigation with dropdown menu
- Dark/light mode toggle
- Mobile-responsive design with sticky header
- All tools working with copy/paste functionality

node_modules/es-abstract/2017/CanonicalNumericIndexString.js

@@ -0,0 +1,19 @@
+'use strict';
+
+var $TypeError = require('es-errors/type');
+
+var SameValue = require('./SameValue');
+var ToNumber = require('./ToNumber');
+var ToString = require('./ToString');
+
+// https://262.ecma-international.org/6.0/#sec-canonicalnumericindexstring
+
+module.exports = function CanonicalNumericIndexString(argument) {
+	if (typeof argument !== 'string') {
+		throw new $TypeError('Assertion failed: `argument` must be a String');
+	}
+	if (argument === '-0') { return -0; }
+	var n = ToNumber(argument);
+	if (SameValue(ToString(n), argument)) { return n; }
+	return void 0;
+};