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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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