Introduction
Builded Omit type can be very useful
e.g.:
interface Obj {
key1: string;
key2: number;
}
type R1 = Omit<Obj, 'key1'>; // { key2: number }
type R2 = Omit<Obj, 'key2'>; // { key1: string }
However there's one disadvantage.
interface Obj {
key1: string;
key2: number;
}
type R1 = Omit<Obj, 'kye1'>; // { key1: string; key2: number }
Omitting a key that doesn't exist is pointless, so I'll expect some error.
Implementation
Omit type looks like this:
type Omit<T, K extends keyof any> = Pick<T, Exclude<keyof T, K>>;
Problem is that K is not key of anything, it's a key of this object. So let's change it:
// type.utils.ts
export type Omit2<T extends {}, K extends keyof T> = Pick<T, Exclude<keyof T, K>>;
interface Obj {
key1: string;
key2: number;
}
type R1 = Omit2<Obj, 'kye1'>; // Type '"kye1"' does not satisfy the constraint 'keyof Obj'.(2344)
Installation
Now we have to ensure that Omit2 will be used instead of Omit. I've no idea how to overwrite something from es5.d.ts, however we can ban Omit using eslint.
// eslintrc.js
module.exports = {
parser: '@typescript-eslint/parser',
plugins: ['@typescript-eslint'],
rules: {
"@typescript-eslint/ban-types": [
"error",
{
"types": {
"Omit": "Use Omit2 from type.utils instead",
},
"extendDefaults": true
}
]
}
Then if someone forgot about the presence of Omit2 eslint will throw an error with a proper message.
Summary
It's not a big improvement but maybe it will catch a bug or two.
Read more
Checkout discussion about strict-ness of Omit. https://github.com/microsoft/TypeScript/issues/30825
Top comments (4)
Or just don't use Omit dev.to/skyjur/your-code-probably-d...
If you decide to abandon Omit, you can use
ban-typesrule from last snippet to enforce that. However I don't recommend that.Interesting idea, didn't think about it but indeed in many projects it could be profitable to add
Omit- to banned types by default - since my observation is that it's been misused more often than it improved anything. Something developers need to understand is that as time passes languages acquire more and more features. Not all features is necessary in every project. It is smart to select small subset of features and techniques that you'll use in your project instead of opt in for everything that community has ever invented.Oh, complexity of TypeScript is a topic for another conversation :D