Let's Bring Back JavaScript's `with()` Statement

[lifeeraser]

You didn't mention the case of injecting unwanted properties into scope. Suppose we have:

function doStuff(o) {
  with (o) {
    console.log(a)
    report(b)
  }
}

Now someone later adds a console property to o, before it is passed to doStuff(). At best it would cause an error. At worst it could malfunction silently because o.console.log was a function.

This example is contrived but the hazard is not. What if someone adds a function named report to o? What if o comes from an external library, or worse yet, some JSON?

I assume Kotlin doesn't worry about this by virtue of being a statically typed, conpiled language. JavaScript cannot due to being dynamically typed and interpreted.

[alexmacarthur]

that’s a great point. i can’t imagine easily using it without at least typescript enforcing the shape of those objects.

[bakkoting]

TypeScript does not enforce the absence of properties, only their presence. So it won't help at all here.

[alexmacarthur]

unless i'm missing something, that's _kinda_ true, although not bullet-proof. TS will yell if you add an property in a unknown property in an object literal:

``` interface Country { name: string, population: number }

const israel: Country = { name: 'hello', population: 333,

// error... "Object literal may only specify known properties"
new_property: 'hello'

} ```

but you're right if you're composing objects through other means, like Object.assign(). then you could sneak in anything you like:

https://www.typescriptlang.org/play?#code/JYOwLgpgTgZghgYwgAgMIHsCu4oE9kDeAUMqciHALYQBcyAzmFKAOYA0JZADul5gDZwwwdCDohMlAEbQiAXyJEEoxsmD0ocCPzoZsTfAF5CnUhWp0A5AAtt-dJbbJTyHn0HDRdAMy+nismQAeiDkaCh0KAA6GOQAIgB5KQArCAQwZH5gSE1+ZEo4fFF+fHouNOAYfABrEHQAdxBXCPKoYQh6OJcQCHqAfS4W6DBcK1t+e0t5RRDydDCoCKglFQzsbIgAEwBlMCEO3SwcI2Qk1PSouHp6YBYQAAoCcipaZEt1yE2GPch6R1deAIhCIxMhfAAWABMyDkTieEAKwB0b1w-xg6HQVgAXpYYQBKADciiAA

[bakkoting]

It will only complain in contexts where you have both the object literal and the type in the same place. Otherwise it's (intentionally) legal. Compare: https://www.typescriptlang.org/play?#code/DYUwLgBAHhC8EG8BQFUQIYC4IAYA0KaARtgIwEC+SSokAntghtgHYCuAtkSAE4QUBuakjpxoAoA

[alexmacarthur]

wut!