how to use the transform function from the lodash library in typescript

To use the transform function from the lodash library in TypeScript, you need to first install the @types/lodash package to ensure correct type definitions are available.

You can then import the function from the module and use it like so:

index.ts
import { transform } from 'lodash';

interface Person {
  name: string;
  age: number;
}

const people: Person[] = [
  { name: 'John', age: 25 },
  { name: 'Jane', age: 30 },
  { name: 'Jack', age: 35 },
];

const ageSumByName = transform(
  people,
  (result, person) => {
    result[person.name] = (result[person.name] ?? 0) + person.age;
  },
  {}
);

console.log(ageSumByName);
// Output: { 'John': 25, 'Jane': 30, 'Jack': 35 }
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24 lines

The first argument to transform is the collection to iterate over, and the second argument is the function that defines the transformation logic. The third argument is the initial value of the accumulator object.

Generics and type inference can also be used to provide type safety and improve readability:

index.ts
const ageSumByName: Record<string, number> = transform<Person, Record<string, number>>(
  people,
  (result, person) => {
    result[person.name] = (result[person.name] ?? 0) + person.age;
  },
  {}
);

console.log(ageSumByName);
// Output: { 'John': 25, 'Jane': 30, 'Jack': 35 }
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11 lines

Here, we're using the Record utility type to define the shape of our accumulator object. The first generic parameter of transform specifies the type of the collection being iterated over, and the second parameter specifies the type of the accumulator object. The return value of transform is automatically inferred from the type of the accumulator object.