/**
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* @fileoverview Ensures that the results of typeof are compared against a valid string
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* @author Ian Christian Myers
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*/
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"use strict";
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//------------------------------------------------------------------------------
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// Rule Definition
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//------------------------------------------------------------------------------
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module.exports = {
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meta: {
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type: "problem",
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docs: {
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description: "enforce comparing `typeof` expressions against valid strings",
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category: "Possible Errors",
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recommended: true,
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url: "https://eslint.org/docs/rules/valid-typeof"
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},
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schema: [
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{
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type: "object",
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properties: {
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requireStringLiterals: {
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type: "boolean",
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default: false
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}
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},
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additionalProperties: false
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}
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],
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messages: {
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invalidValue: "Invalid typeof comparison value.",
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notString: "Typeof comparisons should be to string literals."
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}
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},
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create(context) {
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const VALID_TYPES = ["symbol", "undefined", "object", "boolean", "number", "string", "function", "bigint"],
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OPERATORS = ["==", "===", "!=", "!=="];
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const requireStringLiterals = context.options[0] && context.options[0].requireStringLiterals;
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/**
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* Determines whether a node is a typeof expression.
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* @param {ASTNode} node The node
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* @returns {boolean} `true` if the node is a typeof expression
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*/
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function isTypeofExpression(node) {
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return node.type === "UnaryExpression" && node.operator === "typeof";
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}
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//--------------------------------------------------------------------------
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// Public
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//--------------------------------------------------------------------------
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return {
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UnaryExpression(node) {
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if (isTypeofExpression(node)) {
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const parent = context.getAncestors().pop();
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if (parent.type === "BinaryExpression" && OPERATORS.indexOf(parent.operator) !== -1) {
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const sibling = parent.left === node ? parent.right : parent.left;
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if (sibling.type === "Literal" || sibling.type === "TemplateLiteral" && !sibling.expressions.length) {
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const value = sibling.type === "Literal" ? sibling.value : sibling.quasis[0].value.cooked;
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if (VALID_TYPES.indexOf(value) === -1) {
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context.report({ node: sibling, messageId: "invalidValue" });
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}
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} else if (requireStringLiterals && !isTypeofExpression(sibling)) {
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context.report({ node: sibling, messageId: "notString" });
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}
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}
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}
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}
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};
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}
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};
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