add all frontend files

node_modules/es-abstract/helpers/isPrefixOf.js

@@ -0,0 +1,13 @@
+'use strict';
+
+var $strSlice = require('call-bound')('String.prototype.slice');
+
+module.exports = function isPrefixOf(prefix, string) {
+	if (prefix === string) {
+		return true;
+	}
+	if (prefix.length > string.length) {
+		return false;
+	}
+	return $strSlice(string, 0, prefix.length) === prefix;
+};