no-negated-condition.js
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/**
* @fileoverview Rule to disallow a negated condition
* @author Alberto Rodríguez
*/
"use strict";
//------------------------------------------------------------------------------
// Rule Definition
//------------------------------------------------------------------------------
/** @type {import('../shared/types').Rule} */
module.exports = {
meta: {
type: "suggestion",
docs: {
description: "Disallow negated conditions",
recommended: false,
url: "https://eslint.org/docs/rules/no-negated-condition"
},
schema: [],
messages: {
unexpectedNegated: "Unexpected negated condition."
}
},
create(context) {
/**
* Determines if a given node is an if-else without a condition on the else
* @param {ASTNode} node The node to check.
* @returns {boolean} True if the node has an else without an if.
* @private
*/
function hasElseWithoutCondition(node) {
return node.alternate && node.alternate.type !== "IfStatement";
}
/**
* Determines if a given node is a negated unary expression
* @param {Object} test The test object to check.
* @returns {boolean} True if the node is a negated unary expression.
* @private
*/
function isNegatedUnaryExpression(test) {
return test.type === "UnaryExpression" && test.operator === "!";
}
/**
* Determines if a given node is a negated binary expression
* @param {Test} test The test to check.
* @returns {boolean} True if the node is a negated binary expression.
* @private
*/
function isNegatedBinaryExpression(test) {
return test.type === "BinaryExpression" &&
(test.operator === "!=" || test.operator === "!==");
}
/**
* Determines if a given node has a negated if expression
* @param {ASTNode} node The node to check.
* @returns {boolean} True if the node has a negated if expression.
* @private
*/
function isNegatedIf(node) {
return isNegatedUnaryExpression(node.test) || isNegatedBinaryExpression(node.test);
}
return {
IfStatement(node) {
if (!hasElseWithoutCondition(node)) {
return;
}
if (isNegatedIf(node)) {
context.report({
node,
messageId: "unexpectedNegated"
});
}
},
ConditionalExpression(node) {
if (isNegatedIf(node)) {
context.report({
node,
messageId: "unexpectedNegated"
});
}
}
};
}
};