eslint/lib/rules/max-nested-callbacks.js

An AST-based pattern checker for JavaScript.

/**
 * @fileoverview Rule to enforce a maximum number of nested callbacks.
 * @author Ian Christian Myers
 */

"use strict";

//------------------------------------------------------------------------------
// Requirements
//------------------------------------------------------------------------------

const astUtils = require("./utils/ast-utils");

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

/** @type {import('../types').Rule.RuleModule} */
module.exports = {
	meta: {
		type: "suggestion",

		docs: {
			description: "Enforce a maximum depth that callbacks can be nested",
			recommended: false,
			url: "https://eslint.org/docs/latest/rules/max-nested-callbacks",
		},

		schema: [
			{
				oneOf: [
					{
						type: "integer",
						minimum: 0,
					},
					{
						type: "object",
						properties: {
							maximum: {
								type: "integer",
								minimum: 0,
							},
							max: {
								type: "integer",
								minimum: 0,
							},
							checkConstructorCallCallbacks: {
								type: "boolean",
							},
						},
						additionalProperties: false,
					},
				],
			},
		],

		defaultOptions: [10],

		messages: {
			exceed: "Too many nested callbacks ({{num}}). Maximum allowed is {{max}}.",
		},
	},

	create(context) {
		const sourceCode = context.sourceCode;

		//--------------------------------------------------------------------------
		// Constants
		//--------------------------------------------------------------------------
		const option = context.options[0];
		let THRESHOLD = 10;

		if (
			typeof option === "object" &&
			(Object.hasOwn(option, "maximum") || Object.hasOwn(option, "max"))
		) {
			THRESHOLD = option.maximum || option.max;
		} else if (typeof option === "number") {
			THRESHOLD = option;
		}

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

		const callbackStack = [];

		/**
		 * Checks a given function node for too many callbacks.
		 * @param {ASTNode} node The node to check.
		 * @returns {void}
		 * @private
		 */
		function checkFunction(node) {
			const parent = node.parent;

			if (
				(parent.type !== "CallExpression" &&
					!(
						option.checkConstructorCallCallbacks &&
						parent.type === "NewExpression"
					)) ||
				parent.callee === node
			) {
				return;
			}

			callbackStack.push(node);

			if (callbackStack.length > THRESHOLD) {
				const opts = { num: callbackStack.length, max: THRESHOLD };

				context.report({
					node,
					loc: astUtils.getFunctionHeadLoc(node, sourceCode),
					messageId: "exceed",
					data: opts,
				});
			}
		}

		/**
		 * Pops the call stack.
		 * @param {ASTNode} node The node to check.
		 * @returns {void}
		 * @private
		 */
		function popStack(node) {
			if (callbackStack.at(-1) === node) {
				callbackStack.pop();
			}
		}

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

		return {
			ArrowFunctionExpression: checkFunction,
			"ArrowFunctionExpression:exit": popStack,

			FunctionExpression: checkFunction,
			"FunctionExpression:exit": popStack,
		};
	},
};