Creating an empty array is super easy:
const foo: string[] = [];
If you want to create an array pre-filled with some content use the ES6 Array.prototype.fill
:
const foo: string[] = new Array(3).fill('');
console.log(foo); // ['','',''];
If you want to create an array of a predefined length with calls you can use the spread operator:
const someNumbers = [...new Array(3)].map((_,i) => i * 10);
console.log(someNumbers); // [0,10,20];