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/2021/StringPad.js

@@ -0,0 +1,41 @@
+'use strict';
+
+var $TypeError = require('es-errors/type');
+
+var callBound = require('call-bound');
+
+var ToLength = require('./ToLength');
+var ToString = require('./ToString');
+
+var $strSlice = callBound('String.prototype.slice');
+
+// https://262.ecma-international.org/11.0/#sec-stringpad
+
+module.exports = function StringPad(O, maxLength, fillString, placement) {
+	if (placement !== 'start' && placement !== 'end') {
+		throw new $TypeError('Assertion failed: `placement` must be "start" or "end"');
+	}
+	var S = ToString(O);
+	var intMaxLength = ToLength(maxLength);
+	var stringLength = S.length;
+	if (intMaxLength <= stringLength) {
+		return S;
+	}
+	var filler = typeof fillString === 'undefined' ? ' ' : ToString(fillString);
+	if (filler === '') {
+		return S;
+	}
+	var fillLen = intMaxLength - stringLength;
+
+	// the String value consisting of repeated concatenations of filler truncated to length fillLen.
+	var truncatedStringFiller = '';
+	while (truncatedStringFiller.length < fillLen) {
+		truncatedStringFiller += filler;
+	}
+	truncatedStringFiller = $strSlice(truncatedStringFiller, 0, fillLen);
+
+	if (placement === 'start') {
+		return truncatedStringFiller + S;
+	}
+	return S + truncatedStringFiller;
+};