flow like the river

VISUALIZACION/node_modules/es-abstract/2022/WordCharacters.js

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+'use strict';
+
+var GetIntrinsic = require('get-intrinsic');
+
+var $TypeError = GetIntrinsic('%TypeError%');
+
+var callBound = require('call-bind/callBound');
+var $indexOf = callBound('String.prototype.indexOf', true);
+
+var Canonicalize = require('./Canonicalize');
+var Type = require('./Type');
+
+var caseFolding = require('../helpers/caseFolding');
+var forEach = require('../helpers/forEach');
+var OwnPropertyKeys = require('../helpers/OwnPropertyKeys');
+
+var A = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789_'; // step 1
+
+// https://262.ecma-international.org/8.0/#sec-runtime-semantics-wordcharacters-abstract-operation
+
+module.exports = function WordCharacters(IgnoreCase, Unicode) {
+	if (Type(IgnoreCase) !== 'Boolean' || Type(Unicode) !== 'Boolean') {
+		throw new $TypeError('Assertion failed: `IgnoreCase` and `Unicode` must be booleans');
+	}
+
+	var U = '';
+	forEach(OwnPropertyKeys(caseFolding.C), function (c) {
+		if (
+			$indexOf(A, c) === -1 // c not in A
+			&& $indexOf(A, Canonicalize(c, IgnoreCase, Unicode)) > -1 // canonicalized c IS in A
+		) {
+			U += caseFolding.C[c]; // step 3
+		}
+	});
+	forEach(OwnPropertyKeys(caseFolding.S), function (c) {
+		if (
+			$indexOf(A, c) === -1 // c not in A
+			&& $indexOf(A, Canonicalize(c, IgnoreCase, Unicode)) > -1 // canonicalized c IS in A
+		) {
+			U += caseFolding.S[c]; // step 3
+		}
+	});
+
+	if ((!Unicode || !IgnoreCase) && U.length > 0) {
+		throw new $TypeError('Assertion failed: `U` must be empty when `IgnoreCase` and `Unicode` are not both true'); // step 4
+	}
+
+	return A + U; // step 5, 6
+};