Babel generated Error subclass produces instance of Error rather than instance of subclass

[Gozala]

Input Code

class ReadError extends Error {}

new ReadError('Boom') instanceof ReadError // => false

Babel Configuration (.bablerc, package.json, cli command)

https://babeljs.io/repl/#?babili=false&evaluate=true&lineWrap=false&presets=es2015&experimental=true&loose=false&spec=false&playground=false&code=class%20ReadError%20extends%20Error%20%7B%7D%0A%0Aalert(new%20ReadError('Boom')%20instanceof%20ReadError)%20%2F%2F%20%3D%3E%20false

Expected Behavior

should alert true

Current Behavior

alerts false

[loganfsmyth]

https://stackoverflow.com/questions/33870684/why-doesnt-instanceof-work-on-instances-of-error-subclasses-under-babel-node/33877501#33877501 should cover it.

We mention it here in our Caveats: https://babeljs.io/docs/usage/caveats/#classes but if you have recommendations of a better place let us know.

[forivall]

It's also interesting to note that somehow, it works in node 0.10

https://gist.github.com/forivall/88d8056d87bcc566a5d02ef837d772c6

I'm curious as to how that works, and this could be noted on the caveats page as well.

As far as a better place, it could go in something like "known issues"?

[Gozala]

I would prefer if babel would just error and not compile on attempt to subclass built-ins that can't be. That being said I don't know if work required is worth the benefits.

[hzoo]

We can at least make an option for that (fail when subclassing built-ins)

[xpl]

Try this as a workaround:

class DDoSProtectionError extends Error {
    constructor () {
        super ()
        // a workaround to make `instanceof DDoSProtectionError` work in ES5
        this.constructor = DDoSProtectionError 
        this.__proto__   = DDoSProtectionError.prototype
    }
}

[Leonid-Yeromin]

Almost year, the problem still exists. WTF?

[hzoo]

? You can use #4480 (comment)

[rico345100]

@xpl Worked with 8.x, but not working with 6.9.5
@hzoo Doesn't worked with Node.js 8.9.0

[nicolo-ribaudo]

This should be fixed in Babel 7.

https://babeljs.io/repl/build/master#?babili=false&browsers=last%202%20chrome%20versions%2C%20last%202%20chromeandroid%20versions%2C%20firefox%20esr%2C%20last%202%20firefox%20versions%2C%20edge%20%3E%3D%2015%2C%20safari%20%3E%3D%2011&build=&builtIns=false&code_lz=MYGwhgzhAECC0FMAeAXBA7AJjAogJzwHs9oBvAXwChKwQE8UAKAA0umnQQHc5oBLdBBRh0wBIQBmvALTQAJKU494AoSLGS4Vdkt6rho8VPxESshbpWCDG4wWJVmASgDcQA&debug=false&forceAllTransforms=false&shippedProposals=false&circleciRepo=&evaluate=true&fileSize=false&lineWrap=false&presets=es2015%2Cstage-1&prettier=false&targets=&version=7.0.0-beta.42&envVersion=7.0.0-beta.40%2Bpr.7388

[rico345100]

@nicolo-ribaudo That's awesome. Note that I just fixed this issue.

1. Adding babel-plugin-transform-builtin-extend
2. Do what @xpl suggests

Now it works.