All the source code from this chapter is valid TypeScript code. The difference is that TypeScript will do type checking at compile time to make sure we are only manipulating arrays in which all values have the same datatype.
If we take a look at the preceding code, it is the same numbers array as we declared in previous sections of this chapter:
const numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
Due to the type inference, TypeScript understands that the declaration of the numbers array is the same as const numbers: number[]. For this reason, we do not need to always explicitly declare the variable type if we initialize it during its declaration.
If we go back to the sorting example of the friends array, we can refactor ...
