TypeScript’s discriminated union types (aka tagged union types) allow you to model a finite set of alternative object shapes in the type system. The compiler helps you introduce fewer bugs by only exposing properties that are known to be safe to acce…

Sometimes we want our function arguments to be able to accept more than 1 type; e.g. a string or an array. This lesson will show us how to assign more than 1 type to a variable with Typescript union types and type aliases. type types = string | boole…

关于是否要在 PHP 8 中引入 Union Types 的投票已于近日结束,投票结果显示有 61 名 PHP 开发组成员投了赞成票,5 名投了反对票. 还留意到鸟哥在投票中投了反对票~) 因此根据投票结果,官方已确认将会在 PHP 8 中引入 Union Types 2.0. 关于 Union Types 的具体讨论可在 GitHub 查看,下面我们来简单了解一下 Union Types(联合类型). 根据官方的介绍,Union Types(联合类型)支持接收多个不同类型的值,而不仅仅是单一类…

Typescript 2.5 adds JSDoc type assertion support for javascript file via ts-check service. First of all, you should make sure you have typescript@2.5 install: sudo npm i -g typescript@2.5 Then add @ts-check to the top of js file: // @ts-check This te…

The keyof operator produces a union type of all known, public property names of a given type. You can use it together with lookup types (aka indexed access types) to statically model dynamic property access in the type system. Take away: 1. extends 2…

Mapped types are a powerful and unique feature of TypeScript's type system. They allow you to create a new type by transforming all properties of an existing type according to a given transformation function. In this lesson, we'll cover mapped types…

ypeScript 2.2 introduced the object, a type that represents any non-primitive type. It can be used to more accurately type methods such as Object.create. Don't confuse it with the Object type or {}, the empty object type, though! So one thing we need…

Sometimes the compiler needs help figuring out a type. In this lesson we learn how to help out the compiler with Typescript type assertion. We have a SuperHero and a BadGuy. Let's make a function that saves the day if the function's argument is a Sup…

Lookup types, introduced in TypeScript 2.1, allow us to dynamically create types based on the property keys of an object. We'll use the function spyOn from Jest to illustrate how lookup types can type-safe function parameters. Considering this code:…

前言 Union Type和Intersection Type都是将多个类型结合起来的一个等价的"类型",它们并非是实际存在的类型. Union Type Union type(联合类型)使用比特或运算符|进行构造: A | B | C 注意:用|符号来构造Union Type类型只是Java语言的规定,|在这里不代表比特或的含义. 上例中,A | B | C是一个Union type,Union type的含义就是"或",只要满足其中一个即可. 实例:捕获多个异常…