assert.deepEqual assertion error depth limit

[caub]

I think it would be better if the message of assert.deepEqual was not limited to a depth of 3, and could display the first difference between the objects, like some testing libraries do

const assert = require('assert');

assert.deepEqual({
	foo: {
		bar: {
			qux: {
				lolcat: {
					bip: {
						yup: 56
					}
				}
			}
		}
	}
}, {
	foo: {
		bar: {
			qux: {
				lolcat: {
					bip: {
						yup: 56.3
					}
				}
			}
		}
	}
})

// outputs:
// AssertionError [ERR_ASSERTION]: { foo: { bar: { qux: [Object] } } } deepEqual { foo: { bar: { qux: [Object] } } }

A simple implementation example:

const deepEq = (o1, o2) => {
	const keys1 = Object.keys(o1);
	const keys2 = Object.keys(o2);
	if (keys1.length !== keys2.length) {
		assert.deepEqual(o1, o2);
	}
	for (let i=0; i<keys1.length; i++) {
		const v1 = o1[keys1[i]], v2 = o2[keys1[i]];
		if (v1 && typeof v1 === 'object') {
			deepEq(v1, v2);
		} else {
			assert.equal(v1, v2);
		}
	}
};

The current implementation passes the entire objects in the Error, and .toString is limited in 3 in depth I guess

[caub]

I think there needs a different shape of AssertionError for deepEqual, maybe replacing original and expected by a string showing either:

1. the first difference
2. the full diff (under a max number of lines/chars)

in both case, it could be worth to represent (possibly deep) object paths maybe like:

- foo.bar.qux.lolcat.bip.yup: 56
+ foo.bar.qux.lolcat.bip.yup: 56.3

or

- foo: {bar: {qux: {lolcat: {bip: {yup: 56
+ foo: {bar: {qux: {lolcat: {bip: {yup: 56.3

What are the thoughts? I'll be glad to try to implement it

[joyeecheung]

Not really object to this idea, but there is already power-assert that basically does the same thing (with very fancy diffs)

[caub]

I checked power-assert, it's fancy, but I think a simple approach can be worth for this specific case of object compaisons (not expressions, ...)

https://repl.it/Mqyy/4

deepEqual({
	foo: {
		bar: {
			qux: {
				lolcat: {
					bip: {
						yup: 56.3
					}
				},
				mlop: {}
			}
		}
	}
}, {
	foo: {
		bar: {
			qux: {
				lolcat: {
					bip: {
						yup: 56
					}
				},
				mlep: {
					cool: 'tes',
					flip: 878.964
				}
			}
		}
	}
})

Error: ≠ [foo,bar,qux,lolcat,bip,yup]: 56.3 !== 56
 - [foo,bar,qux,mlop]: {}
 + [foo,bar,qux,mlep]: {"cool":"tes","flip"..
 at ..stacktrace... line...

[caub]

I made this: https://github.com/caub/deep-eq.

Power-assert is cool indeed, but requires transpiling, etc..

I'd still like possibly to change node's assert deepEqual, because it's there by default, and it's really not practical

[BridgeAR]

This got fixed by two PRs: #17615 (strict mode) and #17907 (non strict mode). The object might still be cut off though due to being very big.

[BridgeAR]

Note: Node.js assert(value) got also improved (#17581) and is somewhat similar to the power-assert one, even though not as sophisticated.