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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;
}
};
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