Array Type-Checking

[thomashuston]

In migrating an HTTP test suite that uses node-fetch from Mocha to Jest, a number of tests starting failing when trying to make assertions on cookies. When I dug into it, I traced it back to this Array type check in Headers.

Basically, because Jest executes tests in a vm, the class instances of core types like Array are different from those within Node's libraries like http, so instanceof checks against them fail.

The recommended approach for checking if an object is an array is to instead use the Array.isArray function.

This PR also includes a fallback for old versions of Node that don't include Array.isArray for maximum backwards compatibility.

[codecov-io]

Current coverage is 100% (diff: 100%)

No coverage report found for master at d708acf.

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[bitinn]

This makes sense, I will look into it when available. (From my phone)

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[bitinn]

@TimothyGu I don't consider this a bug per se, do you want to fix it in v2 branch? It got babel for transpiling right?

[TimothyGu]

@bitinn, yeah, sure.

@thomashuston, is the Object.prototype.toString.call(obj) == '[object Array]' check necessary? In other words, is Array.isArray sufficient for it to work?

[thomashuston]

@TimothyGu You're correct, we can just use Array.isArray. I just verified that it was present as far back as Node 0.10. Will update.

[TimothyGu]

Seems like this problem is already fixed in v2 branch, so PR closed. Thanks for the heads-up though.