How to adopt a static typing?

st_example-1.ts

//* Type Inference *//
// The system can guess that array will contain only numbers
// based on the array's initialization.

const arr1 = [14, 21, 28];

arr1.push(15);
arr1.push("Hello World!");



// Type Inference is going to set the type to 'any'
// because we initialize an empty array

const arr2 = [];

arr2.push(27);
arr2.push("Hi there!");



// Type Annotation is a must in this case

let arr3: number[];

arr3.push(77);
arr3.push("It's a string!");