I just found the answer to this in another Stack Overflow question's answer.
declare global {
interface Window { MyNamespace: any; }
}
window.MyNamespace = window.MyNamespace || {};
Basically, you need to extend the existing window
interface to tell it about your new property.
TypeScript uses getter/setter syntax that is like ECMAScript4/ActionScript3.
class foo {
private _bar: boolean = false;
get bar(): boolean {
return this._bar;
}
set bar(value: boolean) {
this._bar = value;
}
}
That will produce this JavaScript, using the ECMAScript 5 Object.defineProperty()
feature.
var foo = (function () {
function foo() {
this._bar = false;
}
Object.defineProperty(foo.prototype, "bar", {
get: function () {
return this._bar;
},
set: function (value) {
this._bar = value;
},
enumerable: true,
configurable: true
});
return foo;
})();
So to use it,
var myFoo = new foo();
if(myFoo.bar) { // calls the getter
myFoo.bar = false; // calls the setter and passes false
}
However, in order to use it at all, you must make sure the TypeScript compiler targets ECMAScript5. If you are running the command line compiler, use --target
flag like this;
tsc --target ES5
If you are using Visual Studio, you must edit your project file to add the flag to the configuration for the TypeScriptCompile build tool. You can see that here:
As @DanFromGermany suggests below, if your are simply reading and writing a local property like foo.bar = true
, then having a setter and getter pair is overkill. You can always add them later if you need to do something, like logging, whenever the property is read or written.
Getters can be used to implement readonly properties. Here is an example that also shows how getters interact with readonly and optional types.
//
// type with optional readonly property.
// baz?:string is the same as baz:string|undefined
//
type Foo = {
readonly bar: string;
readonly baz?: string;
}
const foo:Foo = {bar: "bar"}
console.log(foo.bar) // prints 'bar'
console.log(foo.baz) // prints undefined
//
// interface with optional readonly property
//
interface iFoo {
readonly bar: string;
readonly baz?: string;
}
const ifoo:iFoo = {bar: "bar"}
console.log(ifoo.bar) // prints 'bar'
console.log(ifoo.baz) // prints undefined
//
// class implements bar as a getter,
// but leaves off baz.
//
class iBarClass implements iFoo {
get bar() { return "bar" }
}
const iBarInstance = new iBarClass()
console.log(iBarInstance.bar) // prints 'bar'
// accessing bas gives warning that bas does not exist
// on iBarClass but returns undefined
console.log(iBarInstance.bas) // prints 'undefined'
// note that you could define baz as a getter
// and just return undefined to remove the warning.
//
// class implements optional readonly property as a getter
//
class iBazClass extends iBarClass {
private readonly _baz?: string
constructor(baz?:string) {
super()
this._baz = baz
}
get baz() { return this._baz; }
}
const iBazInstance = new iBazClass("baz")
console.log(iBazInstance.bar) // prints bar
console.log(iBazInstance.baz) // prints baz
Best Answer
Updated 07/12/2016: Typescript 2.1 introduces Mapped Types and provides
Partial<T>
, which allows you to do this....Original Answer:
My approach is to define a separate
fields
variable that you pass to the constructor. The trick is to redefine all the class fields for this initialiser as optional. When the object is created (with its defaults) you simply assign the initialiser object ontothis
;or do it manually (bit more safe):
usage:
and console output:
This gives you basic safety and property initialization, but its all optional and can be out-of-order. You get the class's defaults left alone if you don't pass a field.
You can also mix it with required constructor parameters too -- stick
fields
on the end.About as close to C# style as you're going to get I think (actual field-init syntax was rejected). I'd much prefer proper field initialiser, but doesn't look like it will happen yet.
For comparison, If you use the casting approach, your initialiser object must have ALL the fields for the type you are casting to, plus don't get any class specific functions (or derivations) created by the class itself.