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