no-extend-native.js
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/**
* @fileoverview Rule to flag adding properties to native object's prototypes.
* @author David Nelson
*/
"use strict";
//------------------------------------------------------------------------------
// Requirements
//------------------------------------------------------------------------------
const astUtils = require("./utils/ast-utils");
const globals = require("globals");
//------------------------------------------------------------------------------
// Helpers
//------------------------------------------------------------------------------
const propertyDefinitionMethods = new Set(["defineProperty", "defineProperties"]);
//------------------------------------------------------------------------------
// Rule Definition
//------------------------------------------------------------------------------
module.exports = {
meta: {
type: "suggestion",
docs: {
description: "disallow extending native types",
category: "Best Practices",
recommended: false,
url: "https://eslint.org/docs/rules/no-extend-native"
},
schema: [
{
type: "object",
properties: {
exceptions: {
type: "array",
items: {
type: "string"
},
uniqueItems: true
}
},
additionalProperties: false
}
],
messages: {
unexpected: "{{builtin}} prototype is read only, properties should not be added."
}
},
create(context) {
const config = context.options[0] || {};
const exceptions = new Set(config.exceptions || []);
const modifiedBuiltins = new Set(
Object.keys(globals.builtin)
.filter(builtin => builtin[0].toUpperCase() === builtin[0])
.filter(builtin => !exceptions.has(builtin))
);
/**
* Reports a lint error for the given node.
* @param {ASTNode} node The node to report.
* @param {string} builtin The name of the native builtin being extended.
* @returns {void}
*/
function reportNode(node, builtin) {
context.report({
node,
messageId: "unexpected",
data: {
builtin
}
});
}
/**
* Check to see if the `prototype` property of the given object
* identifier node is being accessed.
* @param {ASTNode} identifierNode The Identifier representing the object
* to check.
* @returns {boolean} True if the identifier is the object of a
* MemberExpression and its `prototype` property is being accessed,
* false otherwise.
*/
function isPrototypePropertyAccessed(identifierNode) {
return Boolean(
identifierNode &&
identifierNode.parent &&
identifierNode.parent.type === "MemberExpression" &&
identifierNode.parent.object === identifierNode &&
astUtils.getStaticPropertyName(identifierNode.parent) === "prototype"
);
}
/**
* Checks that an identifier is an object of a prototype whose member
* is being assigned in an AssignmentExpression.
* Example: Object.prototype.foo = "bar"
* @param {ASTNode} identifierNode The identifier to check.
* @returns {boolean} True if the identifier's prototype is modified.
*/
function isInPrototypePropertyAssignment(identifierNode) {
return Boolean(
isPrototypePropertyAccessed(identifierNode) &&
identifierNode.parent.parent.type === "MemberExpression" &&
identifierNode.parent.parent.parent.type === "AssignmentExpression" &&
identifierNode.parent.parent.parent.left === identifierNode.parent.parent
);
}
/**
* Checks that an identifier is an object of a prototype whose member
* is being extended via the Object.defineProperty() or
* Object.defineProperties() methods.
* Example: Object.defineProperty(Array.prototype, "foo", ...)
* Example: Object.defineProperties(Array.prototype, ...)
* @param {ASTNode} identifierNode The identifier to check.
* @returns {boolean} True if the identifier's prototype is modified.
*/
function isInDefinePropertyCall(identifierNode) {
return Boolean(
isPrototypePropertyAccessed(identifierNode) &&
identifierNode.parent.parent.type === "CallExpression" &&
identifierNode.parent.parent.arguments[0] === identifierNode.parent &&
identifierNode.parent.parent.callee.type === "MemberExpression" &&
identifierNode.parent.parent.callee.object.type === "Identifier" &&
identifierNode.parent.parent.callee.object.name === "Object" &&
identifierNode.parent.parent.callee.property.type === "Identifier" &&
propertyDefinitionMethods.has(identifierNode.parent.parent.callee.property.name)
);
}
/**
* Check to see if object prototype access is part of a prototype
* extension. There are three ways a prototype can be extended:
* 1. Assignment to prototype property (Object.prototype.foo = 1)
* 2. Object.defineProperty()/Object.defineProperties() on a prototype
* If prototype extension is detected, report the AssignmentExpression
* or CallExpression node.
* @param {ASTNode} identifierNode The Identifier representing the object
* which prototype is being accessed and possibly extended.
* @returns {void}
*/
function checkAndReportPrototypeExtension(identifierNode) {
if (isInPrototypePropertyAssignment(identifierNode)) {
// Identifier --> MemberExpression --> MemberExpression --> AssignmentExpression
reportNode(identifierNode.parent.parent.parent, identifierNode.name);
} else if (isInDefinePropertyCall(identifierNode)) {
// Identifier --> MemberExpression --> CallExpression
reportNode(identifierNode.parent.parent, identifierNode.name);
}
}
return {
"Program:exit"() {
const globalScope = context.getScope();
modifiedBuiltins.forEach(builtin => {
const builtinVar = globalScope.set.get(builtin);
if (builtinVar && builtinVar.references) {
builtinVar.references
.map(ref => ref.identifier)
.forEach(checkAndReportPrototypeExtension);
}
});
}
};
}
};