how to use the findindex function from the underscore library in typescript

One way to use the findIndex function from the Underscore library in TypeScript is by first importing it:

index.ts
import { findIndex } from 'underscore';
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Then, assuming you have an array of objects, you can use the findIndex function to search for the index of an object that meets a certain condition. For example, let's say you have an array of Person objects defined like this:

index.ts
interface Person {
  name: string;
  age: number;
}

const people: Person[] = [
  { name: 'Alice', age: 25 },
  { name: 'Bob', age: 30 },
  { name: 'Charlie', age: 35 }
];
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You could use the findIndex function to find the index of the first person in the array who is over 30 years old:

index.ts
const index = findIndex(people, person => person.age > 30);
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In this case, the index variable would be set to 2, because the third person in the array (Charlie) is the first one who meets the condition. If no object in the array meets the condition, findIndex returns -1.

Note that the second argument to findIndex is a callback function that takes an element of the array as its parameter and returns a boolean value indicating whether the element meets the condition. In this example, the callback function uses an arrow function expression to check whether the person's age is greater than 30.