flow like the river

VISUALIZACION/node_modules/es-abstract/2023/Canonicalize.js

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+'use strict';
+
+var GetIntrinsic = require('get-intrinsic');
+
+var $TypeError = GetIntrinsic('%TypeError%');
+
+var callBound = require('call-bind/callBound');
+var has = require('has');
+
+var $charCodeAt = callBound('String.prototype.charCodeAt');
+var $toUpperCase = callBound('String.prototype.toUpperCase');
+
+var Type = require('./Type');
+
+var assertRecord = require('../helpers/assertRecord');
+var caseFolding = require('../helpers/caseFolding');
+
+// https://262.ecma-international.org/14.0/#sec-runtime-semantics-canonicalize-ch
+
+module.exports = function Canonicalize(rer, ch) {
+	assertRecord(Type, 'RegExp Record', 'rer', rer);
+	if (Type(ch) !== 'String') {
+		throw new $TypeError('Assertion failed: `ch` must be a character');
+	}
+
+	if (rer['[[Unicode]]'] && rer['[[IgnoreCase]]']) { // step 1
+		if (has(caseFolding.C, ch)) {
+			return caseFolding.C[ch];
+		}
+		if (has(caseFolding.S, ch)) {
+			return caseFolding.S[ch];
+		}
+		return ch; // step 1.b
+	}
+
+	if (!rer['[[IgnoreCase]]']) {
+		return ch; // step 2
+	}
+
+	var u = $toUpperCase(ch); // step 5
+
+	if (u.length !== 1) {
+		return ch; // step 7
+	}
+
+	var cu = u; // step 8
+
+	if ($charCodeAt(ch, 0) >= 128 && $charCodeAt(cu, 0) < 128) {
+		return ch; // step 9
+	}
+
+	return cu; // step 10
+};