Symbol.toPrimitive A method that converts an object to a corresponding primitive value. Called by the ToPrimitive abstract operation.

Add example code Type the following code into app.ts. function sayHello() { const compiler = (document.getElementById("compiler") as HTMLInputElement).value; const framework = (document.getElementById("framework") as HTMLInputElement).value; return `Hello from ${compiler} and ${framework}!`; }

Ambient Namespaces The popular library D3 defines its functionality in a global object called d3. Because this library is loaded through a <script> tag (instead of a module loader), its declaration uses namespaces to define its shape. For the TypeScript compiler to see this shape, we use an ambient namespace declaration. For example, we could begin writing it as follows: D3.d.ts (simplified excerpt) declare namespace D3 { export interface Selectors { select: { (selector: strin

Validators in a single file interface StringValidator { isAcceptable(s: string): boolean; } let lettersRegexp = /^[A-Za-z]+$/; let numberRegexp = /^[0-9]+$/; class LettersOnlyValidator implements StringValidator { isAcceptable(s: string) { return lettersRegexp.test(s); } } class ZipCodeValidator implements StringValidator { isAcceptable(s: string) { return s.length === 5 && numberRegexp.test(s); } } // Some samples to try let strings = ["Hello", "98052", "101"]; /

Test Run the project. You should see a message when you type in the input boxes:

Class Decorators A Class Decorator is declared just before a class declaration. The class decorator is applied to the constructor of the class and can be used to observe, modify, or replace a class definition. A class decorator cannot be used in a declaration file, or in any other ambient context (such as on a declare class). The expression for the class decorator will be called as a function at runtime, with the constructor of the decorated class as its only argument. If the class decorator re

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Re-export to extend Often you will need to extend functionality on a module. A common JS pattern is to augment the original object with extensions, similar to how JQuery extensions work. As we’ve mentioned before, modules do not merge like global namespace objects would. The recommended solution is to not mutate the original object, but rather export a new entity that provides the new functionality. Consider a simple calculator implementation defined in module Calculator.ts. The module also exp

Module Resolution Strategies There are two possible module resolution strategies: Node and Classic. You can use the --moduleResolution flag to specify the module resolution strategy. The default if not specified is Node.

Debug In Edge, press F12 and click the Debugger tab. Look in the first localhost folder, then src/app.ts Put a breakpoint on the line with return. Type in the boxes and confirm that the breakpoint hits in TypeScript code and that inspection works correctly. That’s all you need to know to include basic TypeScript in your ASP.NET project. Next we’ll include Angular and write a simple Angular app.