Despite this having never been supported in TS, I do believe this is actually the first issue requesting support for it. Trailblazing 😅

...I do believe this is actually the first issue requesting support for it...

I actually am still wary of the spaghetti that TS developers will start cooking if it's supported, but these aren't lazy JavaScript developers, so that's somewhat reassuring. I think we just need more feedback from the community.

The with statement is an error in "use strict" js (and therefore modules), so the code you are even allowed to use it in is actually pretty small. Older sloppy-mode scripts is pretty much it.

The with statement is an error in "use strict" js (and therefore modules), so the code you are even allowed to use it in is actually pretty small. Older sloppy-mode scripts is pretty much it.

Refer to my note under the Checklist:

~ This is a runtime feature, but this is already a feature that was implemented in ECMAScript itself (at some point).
Technically, it has not been removed. It is merely disallowed in strict mode.

I stay within modularized code because it actually makes sense.

Note that I am not suggesting that TS support the statement and just remove type annotations like normal, but instead transpile the statement entirely.

// output after running TSC
with ( foo ) {
    console.log(foo.bar, foo.qux);
}

See how it transpiles variable accesses into object lookups, which should have the same result as if it had not used the with statement at all.

Simply letting the with statement pass unaffected is useless, as often times TSC is run in strict mode, meaning with is a runtime error, as you had mentioned.

By design TypeScript cannot alter the runtime behavior of the code so it’s out of the equation to emit something different from the entered JavaScript code except for downleveling.

By design TypeScript cannot alter the runtime behavior of the code so it’s out of the equation to emit something different from the entered JavaScript code except for downleveling.

But this is a syntax level part of ECMAScript, just like async/await is, we could classify it as down leveling due to it not being supported by our output target (ES5+). (More like the opposite of down leveling, but you get the idea.)

Downleveling would be type-directed emit, so if your request is that, it's out of scope

Dang, guess this classifies as "out of scope" :(

Update this can be done without type based code emit.

input:

const foo = {
    bar: "baz",
    qux: "foobar"
};

with ( foo ) {
    console.log(bar, qux);
}

output:

const foo = {
    bar: "baz",
    qux: "foobar"
};

{
    const __with_scope_0 = foo;

    console.log(
        "bar" in __with_scope_0 ? __with_scope_0.bar : bar,
        "qux" in __with_scope_0 ? __with_scope_0.qux : qux
    );
    // (: bar) in the conditional operator accesses the outer scope's "bar"
}

Example of nested withs:
input:

with ( foo ) {
    with ( bar ) {
        console.log(a);
    }
}

output:

{
    const __with_scope_0 = foo;
    {
        const __with_scope_1 = bar;
        console.log(
            'a' in __with_scope_1 ? __with_scope_1.a : ('a' in __with_scope_0 ? __with_scope_0.a : a)
        );
    }
}

It should always be possible to transpile like this, because JS identifiers are always representable as constant strings, and are always static in the scope. Even if the user brings arbitrary identifiers into scope via eval(), it would be found in the last section of the conditional operator.

The number of with scopes is always static and able to be emit at compile-time, as they cannot be introduced dynamically (e.g. via function calls), and they aren't be able to leak variables outside of their scope.

Furthermore, types can also be resolved as unions of everything that the conditional operations would return!

I am the maintainer of the official Vue IDE plugin. Due to the particularity of the Vue template syntax, we need to use the with statement to make some very important performance improvements. Considering the number of Vue users, the benefits this brings will be huge. If TS can support this, we would be very grateful. 🙏