version 4.17.1，the type of the data variable is inferred to never by _.has

[xujintai123]

issue：
on 4.17.1 version，the type of the data variable is inferred to never by _.has。

source of problem：
#69291
1c01676#diff-0740e38db2dd38b18fb8612ceef08349585a3d898fb6ad21522819b8677804f7

[aj-r]

I'm surprised it narrows the type to never - we have tests to ensure the type remains T when _.has returns false.

I'm guessing the issue is that data's type requires level to be set, so our type guard simplifies to object is T. Thus typescript thinks _.has can never return false, which would be correct as far as the type system is concerned.

Why do you need to use _.has() in this case? Can you simply remove it and assume the property is set? If not, consider changing the type to make the property optional. Or use Object.hasOwnProperty() instead.

[aj-r]

Ah, I just noticed #69534 which should fix this.

[xujintai123]

I'm surprised it narrows the type to never - we have tests to ensure the type remains T when _.has returns false.

I'm guessing the issue is that data's type requires level to be set, so our type guard simplifies to object is T. Thus typescript thinks _.has can never return false, which would be correct as far as the type system is concerned.

Why do you need to use _.has() in this case? Can you simply remove it and assume the property is set? If not, consider changing the type to make the property optional. Or use Object.hasOwnProperty() instead.

its historical code，cause compilation error after upgrade to 4.17.1.

[tidhar-ziv]

This issue is still not solved in version 4.17.4

import _ from "lodash";

function test(doc: any) {
    if (_.has(doc, "something")) {
    }
    else {
        doc["something"] = true;
    }
}

This code will trigger "TS2322: Type 'boolean' is not assignable to type 'never'."

[aj-r]

That seems like reasonable behavior IMHO - if TS thinks the propery doesn't exist then it won't let you set it. If you want to treat the object as a map, use something like Record<string, boolean> (or maybe Record<string, any>) instead of any.

[tidhar-ziv]

equivalent non lodash code doesn't give an error:

function test(doc: any) {
    if (doc.hasOwnProperty("something")) {
    }
    else {
        doc["something"] = true;
    }
}

the type of doc is "any", why would _.has change that? not sure it's lodash job to "discipline" developers, so shouldn't be too opinionated regarding the use of "any". Anyway this is a breaking change, as that was not the behavior prior to version 4.17.1