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/**
* @fileoverview Rule to flag comparisons to the value NaN
* @author James Allardice
*/
"use strict";
//------------------------------------------------------------------------------
// Requirements
//------------------------------------------------------------------------------
const astUtils = require("./utils/ast-utils");
//------------------------------------------------------------------------------
// 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
},
enforceForIndexOf: {
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.",
indexOfNaN: "Array prototype method '{{ methodName }}' cannot find NaN."
}
},
create(context) {
const enforceForSwitchCase = context.options[0] && context.options[0].enforceForSwitchCase;
const enforceForIndexOf = context.options[0] && context.options[0].enforceForIndexOf;
/**
* Checks the given `BinaryExpression` node for `foo === NaN` and other comparisons.
* @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 for `switch(NaN)` and `case NaN:`
* @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" });
}
}
}
/**
* Checks the the given `CallExpression` node for `.indexOf(NaN)` and `.lastIndexOf(NaN)`.
* @param {ASTNode} node The node to check.
* @returns {void}
*/
function checkCallExpression(node) {
const callee = node.callee;
if (callee.type === "MemberExpression") {
const methodName = astUtils.getStaticPropertyName(callee);
if (
(methodName === "indexOf" || methodName === "lastIndexOf") &&
node.arguments.length === 1 &&
isNaNIdentifier(node.arguments[0])
) {
context.report({ node, messageId: "indexOfNaN", data: { methodName } });
}
}
}
const listeners = {
BinaryExpression: checkBinaryExpression
};
if (enforceForSwitchCase) {
listeners.SwitchStatement = checkSwitchStatement;
}
if (enforceForIndexOf) {
listeners.CallExpression = checkCallExpression;
}
return listeners;
}
};
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