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/**
* @fileoverview Rule to flag use of implied eval via setTimeout and setInterval
* @author James Allardice
*/
"use strict";
//------------------------------------------------------------------------------
// Rule Definition
//------------------------------------------------------------------------------
module.exports = {
meta: {
type: "suggestion",
docs: {
description: "disallow the use of `eval()`-like methods",
category: "Best Practices",
recommended: false,
url: "https://eslint.org/docs/rules/no-implied-eval"
},
schema: []
},
create(context) {
const CALLEE_RE = /^(setTimeout|setInterval|execScript)$/u;
/*
* Figures out if we should inspect a given binary expression. Is a stack
* of stacks, where the first element in each substack is a CallExpression.
*/
const impliedEvalAncestorsStack = [];
//--------------------------------------------------------------------------
// Helpers
//--------------------------------------------------------------------------
/**
* Get the last element of an array, without modifying arr, like pop(), but non-destructive.
* @param {Array} arr What to inspect
* @returns {*} The last element of arr
* @private
*/
function last(arr) {
return arr ? arr[arr.length - 1] : null;
}
/**
* Checks if the given MemberExpression node is a potentially implied eval identifier on window.
* @param {ASTNode} node The MemberExpression node to check.
* @returns {boolean} Whether or not the given node is potentially an implied eval.
* @private
*/
function isImpliedEvalMemberExpression(node) {
const object = node.object,
property = node.property,
hasImpliedEvalName = CALLEE_RE.test(property.name) || CALLEE_RE.test(property.value);
return object.name === "window" && hasImpliedEvalName;
}
/**
* Determines if a node represents a call to a potentially implied eval.
*
* This checks the callee name and that there's an argument, but not the type of the argument.
* @param {ASTNode} node The CallExpression to check.
* @returns {boolean} True if the node matches, false if not.
* @private
*/
function isImpliedEvalCallExpression(node) {
const isMemberExpression = (node.callee.type === "MemberExpression"),
isIdentifier = (node.callee.type === "Identifier"),
isImpliedEvalCallee =
(isIdentifier && CALLEE_RE.test(node.callee.name)) ||
(isMemberExpression && isImpliedEvalMemberExpression(node.callee));
return isImpliedEvalCallee && node.arguments.length;
}
/**
* Checks that the parent is a direct descendent of an potential implied eval CallExpression, and if the parent is a CallExpression, that we're the first argument.
* @param {ASTNode} node The node to inspect the parent of.
* @returns {boolean} Was the parent a direct descendent, and is the child therefore potentially part of a dangerous argument?
* @private
*/
function hasImpliedEvalParent(node) {
// make sure our parent is marked
return node.parent === last(last(impliedEvalAncestorsStack)) &&
// if our parent is a CallExpression, make sure we're the first argument
(node.parent.type !== "CallExpression" || node === node.parent.arguments[0]);
}
/**
* Checks if our parent is marked as part of an implied eval argument. If
* so, collapses the top of impliedEvalAncestorsStack and reports on the
* original CallExpression.
* @param {ASTNode} node The CallExpression to check.
* @returns {boolean} True if the node matches, false if not.
* @private
*/
function checkString(node) {
if (hasImpliedEvalParent(node)) {
// remove the entire substack, to avoid duplicate reports
const substack = impliedEvalAncestorsStack.pop();
context.report({ node: substack[0], message: "Implied eval. Consider passing a function instead of a string." });
}
}
//--------------------------------------------------------------------------
// Public
//--------------------------------------------------------------------------
return {
CallExpression(node) {
if (isImpliedEvalCallExpression(node)) {
// call expressions create a new substack
impliedEvalAncestorsStack.push([node]);
}
},
"CallExpression:exit"(node) {
if (node === last(last(impliedEvalAncestorsStack))) {
/*
* Destroys the entire sub-stack, rather than just using
* last(impliedEvalAncestorsStack).pop(), as a CallExpression is
* always the bottom of a impliedEvalAncestorsStack substack.
*/
impliedEvalAncestorsStack.pop();
}
},
BinaryExpression(node) {
if (node.operator === "+" && hasImpliedEvalParent(node)) {
last(impliedEvalAncestorsStack).push(node);
}
},
"BinaryExpression:exit"(node) {
if (node === last(last(impliedEvalAncestorsStack))) {
last(impliedEvalAncestorsStack).pop();
}
},
Literal(node) {
if (typeof node.value === "string") {
checkString(node);
}
},
TemplateLiteral(node) {
checkString(node);
}
};
}
};
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