add all frontend files

node_modules/es-abstract/2019/SymbolDescriptiveString.js

@@ -0,0 +1,16 @@
+'use strict';
+
+var $TypeError = require('es-errors/type');
+
+var callBound = require('call-bound');
+
+var $SymbolToString = callBound('Symbol.prototype.toString', true);
+
+// https://262.ecma-international.org/6.0/#sec-symboldescriptivestring
+
+module.exports = function SymbolDescriptiveString(sym) {
+	if (typeof sym !== 'symbol') {
+		throw new $TypeError('Assertion failed: `sym` must be a Symbol');
+	}
+	return $SymbolToString(sym);
+};