fix(@angular/cli) - include "dom" lib in root tsconfig.json

[deebloo]

Add "dom" lib to root tsconfig.json. fixes #5046

[filipesilva]

LGTM, but you have to change the commit message since that test is failing. The other two failing tests are flakes.

[deebloo]

@filipesilva done. ha I manged to make a mistake in a 3 char pr 😆

[Meligy]

Can we also add "target": "es5" to this?

I was planning to open a discussion about it, tested in VS Code, tslint fails things like:

get someProperty() {
  return `some calculated value`;
}

Because it says you can only have getters when targeting ES5 or higher.

That's because it can only read the closest tsconfig.json file. tsconfig.app.json means nothing to it.

[deebloo]

@Meligy should the target be es5 or should we bump it straight to es2016 since by default TS allows you to use that syntax?

[Meligy]

target is the output, which for the browser (non-node) stuff needs to be es5. We have libs and polyfills for many ES2015 features, but the syntax that cannot be polyfilled needs to be transpiled to ES5.

That's in theory. In reality it doesn't matter, because tsconfig.spec.json and tsconfig.app.json have their own target values (es6 and es5 respectively). This root file is more just for IDEs etc if I get it right.

So, I think we should set it to the minimum of both files, which is es5.

[Meligy]

To explain it a little further: TypeScript in theory supports targeting es3 (outputting to es3), but each feature in TypeScript is only supported in some targets.

For example, property getters are not supported when targeting es3. async/await in TypeScript 1.x was only supported when targeting es6 not even es5.

If you don't specify anything, the lower value is assumed, which is es3. This is for backwards compatibility,
Just like when you don't specify moduleResolution, it's assumed classic, although everyone is (and should be) using node.

[deebloo]

Makes sense @filipesilva what do you think?

[filipesilva]

Makes sense to me as well.

[deebloo]

updated to add es5 to target

[cexbrayat]

I'm possibly mistaken, but doesn't that mean that we can remove the lib and target from tsconfig.app.json?

See #5111 for an attempt

[filipesilva]

@cexbrayat that's right, yes. I added a request for changes to your PR, the es5 bit still needs to stay for non-ng4 projects.

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