@std/assert/equals - assertEquals() fails with function properties without displaying why

[gohjy]

Describe the bug
@std/assert/equals - assertEquals() always throws when any property or sub-property of its input objects is a function, even if they are otherwise identical. The error message contains no hints or highlighting of the functions at all, making it fairly confusing to figure out what went wrong, especially if the inputs have deeply nested objects.

Steps to Reproduce

import { assertEquals } from "jsr:@std/assert";
Deno.test("Example test", () => assertEquals(
    { x: 1, y: () => console.log(2) },
    { x: 1, y: () => console.log(2) }
));

Output (deno test):

error: AssertionError: Values are not equal.


    [Diff] Actual / Expected


    {
      x: 1,
      y: [Function: y],
    }

Output with colored highlighting (image):

Expected behavior

Either (or both) of:

• The error message indicates that functions cannot be compared
• Function is highlighted in output with an indicator that it can't be compared

Alternatively, an assertEqualsWithoutFunctions() function treating all functions as equal would be welcome too.

Environment

• OS: Windows 11 using WSL (Ubuntu 24.04 LTS)
• deno version: 2.5.6
• std version: @std/assert@1.0.16

[lionel-rowe]

It's not that it will throw whenever a property is a function, it's that its way of testing equality for functions is reference equality (unlike for many other types of values, which are compared structurally). It's not possible to meaningfully compare reference-unequal functions for "structural" equality, due to captured scope:

let fn
{ const a = 1; fn = () => a }
const fn1 = fn
{ const a = 2; fn = () => a }
const fn2 = fn

fn1.name === fn2.name // true
fn1.toString() === fn2.toString() // true
Object.getPrototypeOf(fn1) === Object.getPrototypeOf(fn2) // true
// ...etc

fn1() // 1
fn2() // 2

If anything needs fixing, it's that the diff output should maybe explicitly state when there are invisible differences that weren't captured in the diff, rather than just showing the empty diff.

[gohjy]

Ah I see, thank you for the clarification! Should have thought to try passing the same function to both arguments before reporting this, sorry. Thanks for explaining!