node/tools/eslint/lib/rules/no-negated-condition.js

/**
 * @fileoverview Rule to disallow a negated condition
 * @author Alberto Rodríguez
 * @copyright 2015 Alberto Rodríguez. All rights reserved.
 * See LICENSE file in root directory for full license.
 */
"use strict";

//------------------------------------------------------------------------------
// Rule Definition
//------------------------------------------------------------------------------

module.exports = function(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": function(node) {
            if (!hasElseWithoutCondition(node)) {
                return;
            }

            if (isNegatedIf(node)) {
                context.report(node, "Unexpected negated condition.");
            }
        },
        "ConditionalExpression": function(node) {
            if (isNegatedIf(node)) {
                context.report(node, "Unexpected negated condition.");
            }
        }
    };
};

module.exports.schema = [];