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node_modules/eslint/lib/rules/no-undefined.js

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+/**
+ * @fileoverview Rule to flag references to the undefined variable.
+ * @author Michael Ficarra
+ */
+"use strict";
+
+//------------------------------------------------------------------------------
+// Rule Definition
+//------------------------------------------------------------------------------
+
+module.exports = {
+    meta: {
+        type: "suggestion",
+
+        docs: {
+            description: "disallow the use of `undefined` as an identifier",
+            category: "Variables",
+            recommended: false,
+            url: "https://eslint.org/docs/rules/no-undefined"
+        },
+
+        schema: []
+    },
+
+    create(context) {
+
+        /**
+         * Report an invalid "undefined" identifier node.
+         * @param {ASTNode} node The node to report.
+         * @returns {void}
+         */
+        function report(node) {
+            context.report({
+                node,
+                message: "Unexpected use of undefined."
+            });
+        }
+
+        /**
+         * Checks the given scope for references to `undefined` and reports
+         * all references found.
+         * @param {eslint-scope.Scope} scope The scope to check.
+         * @returns {void}
+         */
+        function checkScope(scope) {
+            const undefinedVar = scope.set.get("undefined");
+
+            if (!undefinedVar) {
+                return;
+            }
+
+            const references = undefinedVar.references;
+
+            const defs = undefinedVar.defs;
+
+            // Report non-initializing references (those are covered in defs below)
+            references
+                .filter(ref => !ref.init)
+                .forEach(ref => report(ref.identifier));
+
+            defs.forEach(def => report(def.name));
+        }
+
+        return {
+            "Program:exit"() {
+                const globalScope = context.getScope();
+
+                const stack = [globalScope];
+
+                while (stack.length) {
+                    const scope = stack.pop();
+
+                    stack.push(...scope.childScopes);
+                    checkScope(scope);
+                }
+            }
+        };
+
+    }
+};