Prevent the use methods similar to eval()

Docs > Code Analysis > Static Analysis Rules > Prevent the use methods similar to eval()

This page is not yet available in Spanish. We are working on its translation.
If you have any questions or feedback about our current translation project, feel free to reach out to us!

Metadata

ID: typescript-best-practices/no-implied-eval

Language: TypeScript

Severity: Warning

Category: Security

Description

JavaScript methods like setTimeout(), setInterval(), or execScript() can accept a string of code as their first argument. This code will be executed at runtime, opening a vector for potential attacks.

It is generally considered a bad practice to execute code at runtime. This rule considers these methods as implied evaluations when their parameter is a piece of code.

Non-Compliant Code Examples

setTimeout("x = 1;");
setTimeout("x = 1;", 100);
setInterval("x = 1;");
execScript("x = 1;");
// const s = 'x=1'; setTimeout(s, 100);
setTimeout(String('x=1'), 100);

// member expressions
window.setTimeout('foo');
window.setInterval('foo');
window['setTimeout']('foo');
window['setInterval']('foo');
window[`setInterval`]('foo');
window.window['setInterval']('foo');
global.setTimeout('foo');
global.setInterval('foo');
global['setTimeout']('foo');
global['setInterval']('foo');
global[`setInterval`]('foo');
global.global['setInterval']('foo');
globalThis.setTimeout('foo');
globalThis.setInterval('foo');

// template literals
setTimeout(`foo${bar}`);
window.setTimeout(`foo${bar}`);
window.window.setTimeout(`foo${bar}`);
global.global.setTimeout(`foo${bar}`);

// string concatenation
setTimeout('foo' + bar);
setTimeout(foo + 'bar');
setTimeout(`foo` + bar);
setTimeout(1 + ';' + 1);
window.setTimeout('foo' + bar);
window.setTimeout(foo + 'bar');
window.setTimeout(`foo` + bar);
window.setTimeout(1 + ';' + 1);
window.window.setTimeout(1 + ';' + 1);
global.setTimeout('foo' + bar);
global.setTimeout(foo + 'bar');
global.setTimeout(`foo` + bar);
global.setTimeout(1 + ';' + 1);
global.global.setTimeout(1 + ';' + 1);
globalThis.setTimeout('foo' + bar);

// gives the correct node when dealing with nesting
setTimeout('foo' + (function() {
   setTimeout(helper);
   execScript('str');
   return 'bar';
})());

window.setTimeout('foo' + (function() {
   setTimeout(helper);
   window.execScript('str');
   return 'bar';
})());

global.setTimeout('foo' + (function() {
   setTimeout(helper);
   global.execScript('str');
   return 'bar';
})());

// Optional chaining
window?.setTimeout('code', 0);
(window?.setTimeout)('code', 0);

Compliant Code Examples

setTimeout();

setTimeout;
setTimeout = foo;
window.setTimeout;
window.setTimeout = foo;
window['setTimeout'];
window['setTimeout'] = foo;
global.setTimeout;
global.setTimeout = foo;
global['setTimeout'];
global['setTimeout'] = foo;
globalThis['setTimeout'] = foo;

window[`SetTimeOut`]('foo', 100);
global[`SetTimeOut`]('foo', 100);
global[`setTimeout${foo}`]('foo', 100);
global[`setTimeout${foo}`]('foo', 100);
globalThis[`setTimeout${foo}`]('foo', 100);

// normal usage
setTimeout(function() { x = 1; }, 100);
setInterval(function() { x = 1; }, 100)
execScript(function() { x = 1; }, 100)
window.setTimeout(function() { x = 1; }, 100);
window.setInterval(function() { x = 1; }, 100);
window.execScript(function() { x = 1; }, 100);
window.setTimeout(foo, 100);
window.setInterval(foo, 100);
window.execScript(foo, 100);
global.setTimeout(function() { x = 1; }, 100);
global.setInterval(function() { x = 1; }, 100);
global.execScript(function() { x = 1; }, 100);
global.setTimeout(foo, 100);
global.setInterval(foo, 100);
global.execScript(foo, 100);
globalThis.setTimeout(foo, 100);

// only checks on top-level statements or window.*
foo.setTimeout('hi')

// identifiers are fine
setTimeout(foo, 10)
setInterval(1, 10)
execScript(2)

// as are function expressions
setTimeout(function() {}, 10)

// setInterval
foo.setInterval('hi')
setInterval(foo, 10)
setInterval(function() {}, 10)

// execScript
foo.execScript('hi')
execScript(foo)
execScript(function() {})

// a binary plus on non-strings doesn't guarantee a string
// setTimeout(foo + bar, 10)

// doesn't check anything but the first argument
setTimeout(foobar, 'buzz')
setTimeout(foobar, foo + 'bar')

// only checks immediate subtrees of the argument
setTimeout(function() { return 'foobar'; }, 10)

// https://github.com/eslint/eslint/issues/7821
setTimeoutFooBar('Foo Bar')

foo.window.setTimeout('foo', 100);
foo.global.setTimeout('foo', 100);
// var window; window.setTimeout('foo', 100);
// var global; global.setTimeout('foo', 100);
// function foo(window) { window.setTimeout('foo', 100); }
// function foo(global) { global.setTimeout('foo', 100); }
foo('', window.setTimeout);
foo('', global.setTimeout);