Why did `startStackFunction` get renamed to `startStackFn` from 8.x to 10.x

[Raynos]

In assert.AssertionError, for some reason options.startStackFunction got renamed to options.startStackFn from v8.x to v10.x

This means you have to do var e = new AssertionError({ startStackFn: fn, startStackFunction: fn }) to have code that works across both versions of nodejs.

This seems like an unnecessary breaking change :( is there no policy or code review for API stability ?

[BridgeAR]

@Raynos that was a mistake on my side. I did not anticipate that the error class would actually really be used in the wild (it was not documented) and that this option would be used. I'll open a PR to accept both as valid options but that will probably not help a lot anymore.

[BridgeAR]

I'll try to backport this as well.

[Raynos]

@BridgeAR you are my hero.

Here is my use case for context.

'use strict'

const process = require('process')
const { AssertionError } = require('assert')

module.exports = nextTickAssert

function nextTickAssert (value, message) {
 let errorToBeThrown

 if (!value) {
 let generatedMessage = false

 if (arguments.length === 0) {
 generatedMessage = true
 message = 'No value argument passed to `assert.ok()`'
 } else if (message == null) {
 generatedMessage = true
 message = String(value) + ' == true'
 }

 if (message instanceof Error) {
 errorToBeThrown = message
 } else {
 const err = new AssertionError({
 message: message,
 actual: value,
 expected: true,
 operator: '==',
 stackStartFunction: nextTickAssert,
 stackStartFn: nextTickAssert
 })
 err.generatedMessage = generatedMessage
 errorToBeThrown = err
 }

 process.nextTick(() => {
 throw errorToBeThrown
 })
 }
}

I want to use assert() but somehow bail outside of async/await; I want sanity assertions that should never happen and fail my program.

I'll open an issue / PR on node core for this seperately as it's a useful issue that came up on twitter a while ago.

[BridgeAR]

@Raynos I believe you actually want to use the --unhandled-rejections=strict mode in that case. That is not yet available in Node.js < 11.x but it should be backported to at least 10.x.

[BridgeAR]

An easier solution would also be the following:

'use strict'

const process = require('process')
const assert = require('assert').strict

module.exports = nextTickAssert

function nextTickAssert (value, message) {
 try {
 assert(value, message)
 } catch (err) {
 Error.captureStackTrace(err, nextTickAssert);
 process.nextTick(() => {
 throw err
 })
 }
}

[Raynos]

Your solution means i don't have an issue with the AssertionError constructor anymore. I didn't think about catching the error ...

I'd have to write some benchmarks though. The existing assert() calls are mostly free because they are a single if branch on a boolean.

[BridgeAR]

@Raynos the cost should be identical in newer Node.js versions. I believe Node.js 8 is already fine with try / catch statements but I forgot in what version the performance cliff got removed.

There is one significant difference between these two versions though: the error message will be different (in case no message argument was passed through). Due to the abstraction, assert is not going to be able to determine the actual call site anymore but you said you want this only as safe guard that should actually never trigger.