no-console.js

/**
 * @fileoverview Rule to flag use of console object
 * @author Nicholas C. Zakas
 */

"use strict";

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

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

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

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

        docs: {
            description: "Disallow the use of `console`",
            recommended: false,
            url: "https://eslint.org/docs/latest/rules/no-console"
        },

        schema: [
            {
                type: "object",
                properties: {
                    allow: {
                        type: "array",
                        items: {
                            type: "string"
                        },
                        minItems: 1,
                        uniqueItems: true
                    }
                },
                additionalProperties: false
            }
        ],

        hasSuggestions: true,

        messages: {
            unexpected: "Unexpected console statement.",
            removeConsole: "Remove the console.{{ propertyName }}()."
        }
    },

    create(context) {
        const options = context.options[0] || {};
        const allowed = options.allow || [];
        const sourceCode = context.sourceCode;

        /**
         * Checks whether the given reference is 'console' or not.
         * @param {eslint-scope.Reference} reference The reference to check.
         * @returns {boolean} `true` if the reference is 'console'.
         */
        function isConsole(reference) {
            const id = reference.identifier;

            return id && id.name === "console";
        }

        /**
         * Checks whether the property name of the given MemberExpression node
         * is allowed by options or not.
         * @param {ASTNode} node The MemberExpression node to check.
         * @returns {boolean} `true` if the property name of the node is allowed.
         */
        function isAllowed(node) {
            const propertyName = astUtils.getStaticPropertyName(node);

            return propertyName && allowed.includes(propertyName);
        }

        /**
         * Checks whether the given reference is a member access which is not
         * allowed by options or not.
         * @param {eslint-scope.Reference} reference The reference to check.
         * @returns {boolean} `true` if the reference is a member access which
         *      is not allowed by options.
         */
        function isMemberAccessExceptAllowed(reference) {
            const node = reference.identifier;
            const parent = node.parent;

            return (
                parent.type === "MemberExpression" &&
                parent.object === node &&
                !isAllowed(parent)
            );
        }

        /**
         * Checks if removing the ExpressionStatement node will cause ASI to
         * break.
         * eg.
         * foo()
         * console.log();
         * [1, 2, 3].forEach(a => doSomething(a))
         *
         * Removing the console.log(); statement should leave two statements, but
         * here the two statements will become one because [ causes continuation after
         * foo().
         * @param {ASTNode} node The ExpressionStatement node to check.
         * @returns {boolean} `true` if ASI will break after removing the ExpressionStatement
         *      node.
         */
        function maybeAsiHazard(node) {
            const SAFE_TOKENS_BEFORE = /^[:;{]$/u; // One of :;{
            const UNSAFE_CHARS_AFTER = /^[-[(/+`]/u; // One of [(/+-`

            const tokenBefore = sourceCode.getTokenBefore(node);
            const tokenAfter = sourceCode.getTokenAfter(node);

            return (
                Boolean(tokenAfter) &&
                UNSAFE_CHARS_AFTER.test(tokenAfter.value) &&
                tokenAfter.value !== "++" &&
                tokenAfter.value !== "--" &&
                Boolean(tokenBefore) &&
                !SAFE_TOKENS_BEFORE.test(tokenBefore.value)
            );
        }

        /**
         * Checks if the MemberExpression node's parent.parent.parent is a
         * Program, BlockStatement, StaticBlock, or SwitchCase node. This check
         * is necessary to avoid providing a suggestion that might cause a syntax error.
         *
         * eg. if (a) console.log(b), removing console.log() here will lead to a
         *     syntax error.
         *     if (a) { console.log(b) }, removing console.log() here is acceptable.
         *
         * Additionally, it checks if the callee of the CallExpression node is
         * the node itself.
         *
         * eg. foo(console.log), cannot provide a suggestion here.
         * @param {ASTNode} node The MemberExpression node to check.
         * @returns {boolean} `true` if a suggestion can be provided for a node.
         */
        function canProvideSuggestions(node) {
            return (
                node.parent.type === "CallExpression" &&
                node.parent.callee === node &&
                node.parent.parent.type === "ExpressionStatement" &&
                astUtils.STATEMENT_LIST_PARENTS.has(node.parent.parent.parent.type) &&
                !maybeAsiHazard(node.parent.parent)
            );
        }

        /**
         * Reports the given reference as a violation.
         * @param {eslint-scope.Reference} reference The reference to report.
         * @returns {void}
         */
        function report(reference) {
            const node = reference.identifier.parent;

            const propertyName = astUtils.getStaticPropertyName(node);

            context.report({
                node,
                loc: node.loc,
                messageId: "unexpected",
                suggest: canProvideSuggestions(node)
                    ? [{
                        messageId: "removeConsole",
                        data: { propertyName },
                        fix(fixer) {
                            return fixer.remove(node.parent.parent);
                        }
                    }]
                    : []
            });
        }

        return {
            "Program:exit"(node) {
                const scope = sourceCode.getScope(node);
                const consoleVar = astUtils.getVariableByName(scope, "console");
                const shadowed = consoleVar && consoleVar.defs.length > 0;

                /*
                 * 'scope.through' includes all references to undefined
                 * variables. If the variable 'console' is not defined, it uses
                 * 'scope.through'.
                 */
                const references = consoleVar
                    ? consoleVar.references
                    : scope.through.filter(isConsole);

                if (!shadowed) {
                    references
                        .filter(isMemberAccessExceptAllowed)
                        .forEach(report);
                }
            }
        };
    }
};