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node_modules/eslint/lib/rules/use-isnan.js

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+/**
+ * @fileoverview Rule to flag comparisons to the value NaN
+ * @author James Allardice
+ */
+
+"use strict";
+
+//------------------------------------------------------------------------------
+// Helpers
+//------------------------------------------------------------------------------
+
+/**
+ * Determines if the given node is a NaN `Identifier` node.
+ * @param {ASTNode|null} node The node to check.
+ * @returns {boolean} `true` if the node is 'NaN' identifier.
+ */
+function isNaNIdentifier(node) {
+    return Boolean(node) && node.type === "Identifier" && node.name === "NaN";
+}
+
+//------------------------------------------------------------------------------
+// Rule Definition
+//------------------------------------------------------------------------------
+
+module.exports = {
+    meta: {
+        type: "problem",
+
+        docs: {
+            description: "require calls to `isNaN()` when checking for `NaN`",
+            category: "Possible Errors",
+            recommended: true,
+            url: "https://eslint.org/docs/rules/use-isnan"
+        },
+
+        schema: [
+            {
+                type: "object",
+                properties: {
+                    enforceForSwitchCase: {
+                        type: "boolean",
+                        default: false
+                    }
+                },
+                additionalProperties: false
+            }
+        ],
+
+        messages: {
+            comparisonWithNaN: "Use the isNaN function to compare with NaN.",
+            switchNaN: "'switch(NaN)' can never match a case clause. Use Number.isNaN instead of the switch.",
+            caseNaN: "'case NaN' can never match. Use Number.isNaN before the switch."
+        }
+    },
+
+    create(context) {
+
+        const enforceForSwitchCase = context.options[0] && context.options[0].enforceForSwitchCase;
+
+        /**
+         * Checks the given `BinaryExpression` node.
+         * @param {ASTNode} node The node to check.
+         * @returns {void}
+         */
+        function checkBinaryExpression(node) {
+            if (
+                /^(?:[<>]|[!=]=)=?$/u.test(node.operator) &&
+                (isNaNIdentifier(node.left) || isNaNIdentifier(node.right))
+            ) {
+                context.report({ node, messageId: "comparisonWithNaN" });
+            }
+        }
+
+        /**
+         * Checks the discriminant and all case clauses of the given `SwitchStatement` node.
+         * @param {ASTNode} node The node to check.
+         * @returns {void}
+         */
+        function checkSwitchStatement(node) {
+            if (isNaNIdentifier(node.discriminant)) {
+                context.report({ node, messageId: "switchNaN" });
+            }
+
+            for (const switchCase of node.cases) {
+                if (isNaNIdentifier(switchCase.test)) {
+                    context.report({ node: switchCase, messageId: "caseNaN" });
+                }
+            }
+        }
+
+        const listeners = {
+            BinaryExpression: checkBinaryExpression
+        };
+
+        if (enforceForSwitchCase) {
+            listeners.SwitchStatement = checkSwitchStatement;
+        }
+
+        return listeners;
+    }
+};