eslint/lib/rules/no-constant-condition.js

/**
 * @fileoverview Rule to flag use constant conditions
 * @author Christian Schulz <http://rndm.de>
 */


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

module.exports = function(context) {

    "use strict";

    // array of types that should always trigger this rule if used inside a condition
    var alwaysSimpleConstantCondition = ["Literal", "FunctionExpression", "ObjectExpression", "ArrayExpression"],
        // map of functions that should be called to determine if it is a constant condition
        sometimesSimpleConstantCondition = {
            /**
             * Checks assignment expression for literal argument.
             * @example returns true for: if (t = +2) { doSomething() }
             * @param {ASTNode} field The AST node to check.
             * @returns {Boolean} true if assignment has right side literal or identifier.
             */
            "AssignmentExpression": function(field) {
                return (field.right.type === "Literal" ||
                    (field.right.type === "UnaryExpression" && field.right.argument.type === "Literal"));
            },
            /**
             * Checks unary expression for literal argument.
             * @example returns true for: if (+2) { doSomething(); }
             * @param {ASTNode} field The AST node to check.
             * @returns {Boolean} true if field has literal argument type.
             */
            "UnaryExpression": function(field) {
                return field.argument.type === "Literal";
            }
        };

    //--------------------------------------------------------------------------
    // Helpers
    //--------------------------------------------------------------------------

    /**
     * Checks if a node contains a constant condition.
     * @param {ASTNode} node The AST node to check.
     * @returns {void}
     * @private
     */
    function checkConstantCondition(node) {
        var field = node.test;
        // check if type exists in simpleConditions array
        if (alwaysSimpleConstantCondition.indexOf(field.type) !== -1 ||
            // check if type exists in sometimes simple conditions
            (sometimesSimpleConstantCondition.hasOwnProperty(field.type) &&
                // check if type is a simple condition
                sometimesSimpleConstantCondition[field.type](field))) {

            context.report(node, "Unexpected constant condition.");
        }
    }

    //--------------------------------------------------------------------------
    // Public
    //--------------------------------------------------------------------------

    return {
        "ConditionalExpression": checkConstantCondition,
        "IfStatement": checkConstantCondition,
        "WhileStatement": checkConstantCondition,
        "DoWhileStatement": checkConstantCondition,
        "ForStatement": checkConstantCondition
    };

};