TypeScript 1.3

Protected #

The new protected modifier in classes works like it does in familiar languages like C++, C#, and Java. A protected member of a class is visible only inside subclasses of the class in which it is declared:

class Thing {
  protected doSomething() { /* ... */ }
}

class MyThing extends Thing {
  public myMethod() {
    // OK, can access protected member from subclass
    this.doSomething();
  }
}
var t = new MyThing();
t.doSomething(); // Error, cannot call protected member from outside class

Tuple types #

Tuple types express an array where the type of certain elements is known, but need not be the same. For example, you may want to represent an array with a string at position 0 and a number at position 1:

// Declare a tuple type
var x: [string, number];
// Initialize it
x = ['hello', 10]; // OK
// Initialize it incorrectly
x = [10, 'hello']; // Error

When accessing an element with a known index, the correct type is retrieved:

console.log(x[0].substr(1)); // OK
console.log(x[1].substr(1)); // Error, 'number' does not have 'substr'

Note that in TypeScript 1.4, when accessing an element outside the set of known indices, a union type is used instead:

x[3] = 'world'; // OK
console.log(x[5].toString()); // OK, 'string' and 'number' both have toString
x[6] = true; // Error, boolean isn't number or string