Protected

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

ts
classThing {
protecteddoSomething() {
/* ... */
  }
}
classMyThingextendsThing {
publicmyMethod() {
// OK, can access protected member from subclass
this.doSomething();
  }
}
vart =newMyThing();
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 astring at position 0 and anumber at position 1:

ts
// Declare a tuple type
varx: [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:

ts
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:

ts
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