Add Readonly Examples

In references to #2702. Making another commit due to several extra files getting committed.
This commit is contained in:
Wayne Boka 2018-10-03 16:23:54 -04:00
parent 648fe48c5a
commit f8ff01a17e

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@ -178,6 +178,37 @@ let greeting = `Hi ${name}, how are you?`
let multiline = `This is an example let multiline = `This is an example
of a multiline string`; of a multiline string`;
// READONLY: New Feature in TypeScript 3.1
interface Person {
readonly name: string;
readonly age: number;
}
var p1: Person = { name: "Tyrone", age: 42 };
p1.age = 25; // Error, p1.x is read-only
var p2 = { name: "John", age: 60 };
var p3: Person = p2; // Ok, read-only alias for p2
p3.x = 35; // Error, p3.x is read-only
p2.x = 45; // Ok, but also changes p3.x because of aliasing
class Car {
readonly make: string;
readonly model: string;
readonly year = 2018;
constructor() {
this.make = "Unknown Make"; // Assignment permitted in constructor
this.model = "Unknown Model"; // Assignment permitted in constructor
}
}
let numbers: Array<number> = [0, 1, 2, 3, 4];
let moreNumbers: ReadonlyArray<number> = numbers;
moreNumbers[5] = 5; // Error, elements are read-only
moreNumbers.push(5); // Error, no push method (because it mutates array)
moreNumbers.length = 3; // Error, length is read-only
numbers = moreNumbers; // Error, mutating methods are missing
``` ```
## Further Reading ## Further Reading