with

Replaces a value at a given key

import { obj } from "@tsly/obj";
 
const person = obj({
    name: { first: "john", last: "smith" },
    age: 25,
});
 
person.with("age", 30).take(console.log);
// { name: { first: "john", last: "smith"} }, age: 30 }
 
// introducing new keys is also typesafe
const updated = person.with('hobbies', ['running']).take();
//    ^? (typeof person) & { hobbies: string[] }

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A mapping function can also be specified instead of a value. This function will be called with the object's previous value at the specified key, and the result of the function will be used as the new value.

import { obj } from "@tsly/obj";
 
const person = obj({
    name: { first: "john", last: "smith" },
    age: 25,
});
 
person.with('age', age => age + 1).take(console.log);
// { name: { first: "john", last: "doe" }, age: 26 }

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When updating subobject values, Typescriptly will automatically wrap the argument of the mapping function with TslyObject so that .with can be chained. These objects are automatically unwrapped when they return from the function, so you don't need to call .take().

import { obj } from "@tsly/obj";
 
const person = obj({
    name: { first: "john", last: "smith" },
    age: 25,
});
 
person
    .with('name', name =>
        name.with("first", 'david')) // <- `name` is auto wrapped/taken as a `TslyObject`
    .take(console.log)
 
// { name: { first: "david", last: "doe" }, age: 25 }

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into Maybe