This issue is to track all the various this proposals floating around and to distinguish them. Any comments here should be clarifying comments/questions.
this as a function return value
Let type definitions specify that the type of a field (or maybe just function return values) is the same as the type that contains the property.
Example:
interface Animal {
clone(): this; // Today: clone(): Animal;
self: this;
}
interface Dog extends Animal { woof(); }
interface Cat extends Animal { meow(); }
var c: Cat;
var cc = c.clone(); // Desired: cc: Cat
cc.meow(); // Desired: OK. Today: Fails
var ccc = cc.self; // Desired: ccc: Cat Specify, as part of a function, the type of this inside the function body
Allow a syntax to specify the type of this as part of a function expression.
Example:
function fn(this: HTMLElement) {
this.focus(); // OK
}
fn(); // 'this' argument not visible externally. May or may not be error Specify, as part of a function type, the type of this inside a function body
(no issue yet, please leave a comment if you create one)
Allow a syntax to specify that when a function is invoked, this will be of a certain type
Example:
// http://api.jquery.com/jquery.each/
function jquery_each<T>(items: T[], callback: (this: T, index: number, value: T) { /* ... */ }
jquery_each(['foo', 'bar'], () => console.log(this.substr(1)); Specify the what valid this values are during function invocation
Add type system logic to detect when a method is being invoked without a proper this context
class Foo {
bar = 5;
printBar() { console.log(this.bar); }
}
var f = new Foo();
// prints 'undefined', not '5'
window.setImmediate(f.printBar); // Flag this as an error
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