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/**
* @fileoverview Rule to disallow negating the left operand of relational operators
* @author Toru Nagashima
*/
"use strict";
//------------------------------------------------------------------------------
// Requirements
//------------------------------------------------------------------------------
const astUtils = require("./utils/ast-utils");
//------------------------------------------------------------------------------
// Helpers
//------------------------------------------------------------------------------
/**
* Checks whether the given operator is a relational operator or not.
*
* @param {string} op - The operator type to check.
* @returns {boolean} `true` if the operator is a relational operator.
*/
function isRelationalOperator(op) {
return op === "in" || op === "instanceof";
}
/**
* Checks whether the given node is a logical negation expression or not.
*
* @param {ASTNode} node - The node to check.
* @returns {boolean} `true` if the node is a logical negation expression.
*/
function isNegation(node) {
return node.type === "UnaryExpression" && node.operator === "!";
}
//------------------------------------------------------------------------------
// Rule Definition
//------------------------------------------------------------------------------
module.exports = {
meta: {
type: "problem",
docs: {
description: "disallow negating the left operand of relational operators",
category: "Possible Errors",
recommended: true,
url: "https://eslint.org/docs/rules/no-unsafe-negation"
},
schema: [],
fixable: null,
messages: {
unexpected: "Unexpected negating the left operand of '{{operator}}' operator."
}
},
create(context) {
const sourceCode = context.getSourceCode();
return {
BinaryExpression(node) {
if (isRelationalOperator(node.operator) &&
isNegation(node.left) &&
!astUtils.isParenthesised(sourceCode, node.left)
) {
context.report({
node,
loc: node.left.loc,
messageId: "unexpected",
data: { operator: node.operator }
});
}
}
};
}
};
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