node/tools/eslint/lib/rules/complexity.js

/**
 * @fileoverview Counts the cyclomatic complexity of each function of the script. See http://en.wikipedia.org/wiki/Cyclomatic_complexity.
 * Counts the number of if, conditional, for, whilte, try, switch/case,
 * @author Patrick Brosset
 */

"use strict";

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

module.exports = function(context) {

    var THRESHOLD = (typeof context.options[0] !== "undefined") ? context.options[0] : 20;

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

    // Using a stack to store complexity (handling nested functions)
    var fns = [];

    /**
     * When parsing a new function, store it in our function stack
     * @returns {void}
     * @private
     */
    function startFunction() {
        fns.push(1);
    }

    /**
     * Evaluate the node at the end of function
     * @param {ASTNode} node node to evaluate
     * @returns {void}
     * @private
     */
    function endFunction(node) {
        var complexity = fns.pop(),
            name = "anonymous";

        if (node.id) {
            name = node.id.name;
        } else if (node.parent.type === "MethodDefinition" || node.parent.type === "Property") {
            name = node.parent.key.name;
        }

        if (complexity > THRESHOLD) {
            context.report(node, "Function '{{name}}' has a complexity of {{complexity}}.", { name: name, complexity: complexity });
        }
    }

    /**
     * Increase the complexity of the function in context
     * @returns {void}
     * @private
     */
    function increaseComplexity() {
        if (fns.length) {
            fns[fns.length - 1] ++;
        }
    }

    /**
     * Increase the switch complexity in context
     * @param {ASTNode} node node to evaluate
     * @returns {void}
     * @private
     */
    function increaseSwitchComplexity(node) {
        // Avoiding `default`
        if (node.test) {
            increaseComplexity(node);
        }
    }

    /**
     * Increase the logical path complexity in context
     * @param {ASTNode} node node to evaluate
     * @returns {void}
     * @private
     */
    function increaseLogicalComplexity(node) {
        // Avoiding &&
        if (node.operator === "||") {
            increaseComplexity(node);
        }
    }

    //--------------------------------------------------------------------------
    // Public API
    //--------------------------------------------------------------------------

    return {
        "FunctionDeclaration": startFunction,
        "FunctionExpression": startFunction,
        "ArrowFunctionExpression": startFunction,
        "FunctionDeclaration:exit": endFunction,
        "FunctionExpression:exit": endFunction,
        "ArrowFunctionExpression:exit": endFunction,

        "CatchClause": increaseComplexity,
        "ConditionalExpression": increaseComplexity,
        "LogicalExpression": increaseLogicalComplexity,
        "ForStatement": increaseComplexity,
        "ForInStatement": increaseComplexity,
        "ForOfStatement": increaseComplexity,
        "IfStatement": increaseComplexity,
        "SwitchCase": increaseSwitchComplexity,
        "WhileStatement": increaseComplexity,
        "DoWhileStatement": increaseComplexity
    };

};

module.exports.schema = [
    {
        "type": "integer",
        "minimum": 0
    }
];