Typescript has two different universes that come into contact in some points: Value space and Type space. Type space is where types are defined and types get erased completely and don’t exist at runtime. Value space contains values and will obviously exist at runtime. What is a value? Value literals, variables, constants and parameters are … Read more
See the reference for user-defined type guard functions for more information. function isString(test: any): test is string{ return typeof test === “string”; } function example(foo: any){ if(isString(foo)){ console.log(“it is a string” + foo); console.log(foo.length); // string function } } example(“hello world”); Using the type predicate test is string in the above format (instead of just … Read more
Simple answer. Use the Angular CLI and issue the ng build command in the root directory of your project. The site will be created in the dist directory and you can deploy that to any web server. This will build for test, if you have production settings in your app you should use ng build … Read more
You’re correct, it’s not currently representable in TypeScript. There’s a longstanding open GitHub feature request, microsoft/TypeScript#1213, which should probably be titled something like “support higher kinded types” but currently has the title “Allow classes to be parametric in other parametric classes”. There are some ideas in the discussion about how to simulate such higher kinded … Read more
The only possible way this could work at compile time is if your arrays are tuples composed of literals. For example, here are some arrays with the same runtime values, but with different types in TypeScript: const tupleOfLiterals: [1, 2, 2] = [1, 2, 2]; const tupleOfNonLiterals: [number, number, number] = [1, 2, 2]; const … Read more
This TypeScript code class A { private a1; public a2; } compiles to this JavaScript code class A { } That’s because properties in JavaScript start extisting only after they have some value. You have to assign the properties some value. class A { private a1 = “”; public a2 = “”; } it compiles … Read more
If You have small range, you can always write something like: type MyRange = 5|6|7|8|9|10 let myVar:MyRange = 4; // oops, error 🙂 Of course it works just for integers and is ugly as hell 🙂
The JavaScript array has a constructor that accepts the length of the array: let arr = new Array<number>(3); console.log(arr); // [undefined × 3] However, this is just the initial size, there’s no restriction on changing that: arr.push(5); console.log(arr); // [undefined × 3, 5] TypeScript has tuple types which let you define an array with a … Read more
TypeScript has three confusing types: Object, {} and object. You can assign null and undefined to all three types if strictNullChecks compiler option is disabled otherwise the compile error occurs. Object Contains stuff (like toString(), hasOwnProperty()) that is present in all JavaScript objects. Any value (primitive, non-primitive) can be assigned to Object type. {} {} … Read more