Learn React with TypeScript 3

Type checking with a type predicate

One way we can perform type checking in a function is with another function that has a return type as a type predicate. Let's explore this and eventually create a new version of our logScores function:

1. First, we'll define a new function called scoresCheck to do the necessary type checking:

const scoresCheck = (  scores: any): scores is { name: string; scores: number[] } => {  return "name" in scores && "scores" in scores;};

This takes in a scores parameter that has a type predicate, scores is { name: string; scores: number[] }, ensuring it contains the correctly typed name and scores properties. The function simply returns whether the scores parameter contains the name and scores properties.

2. Let's use ...