node/tools/eslint/lib/rules/func-style.js

/**
 * @fileoverview Rule to enforce a particular function style
 * @author Nicholas C. Zakas
 * @copyright 2013 Nicholas C. Zakas. All rights reserved.
 */
"use strict";

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

module.exports = function(context) {

    var style = context.options[0],
        enforceDeclarations = (style === "declaration");

    return {

        "FunctionDeclaration": function(node) {
            if (!enforceDeclarations) {
                context.report(node, "Expected a function expression.");
            }
        },

        "FunctionExpression": function() {
            var parent = context.getAncestors().pop();

            if (enforceDeclarations && parent.type === "VariableDeclarator") {
                context.report(parent, "Expected a function declaration.");
            }
        },

        "ArrowFunctionExpression": function() {
            var parent = context.getAncestors().pop();

            if (enforceDeclarations && parent.type === "VariableDeclarator") {
                context.report(parent, "Expected a function declaration.");
            }
        }

    };

};

module.exports.schema = [
    {
        "enum": ["declaration", "expression"]
    }
];