[Typescript] Specify Exact Values with TypeScript’s Literal Types-白红宇

[Typescript] Specify Exact Values with TypeScript’s Literal Types

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发布时间：2019-06-12

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A literal type is a type that represents exactly one value, e.g. one specific string or number. You can combine literal types with union types to model a finite set of valid values for a variable. In this lesson, we explore the all kinds of literal types in TypeScript:

String literal types

Numeric literal types

Boolean literal types

Enum literal types

First String literal types:

let autoComplete: "on" | "off" | "ON" | "OFF";autoComplete = "On" // case sensitive, compiler error

Number literal types:

type NumberBase = 2 | 8 |10 | 16;let base: NumberBase;base = 2;base = 4; // error

Boolean literal types:

let autoFocus: true = true;autoFocus = false; // error

Enum literal types:

enum Protocols {    HTTP,    HTTPS,    FTP}type HyperTextProtocol = Protocols.HTTP | Protocols.HTTPS;let protocol: HyperTextProtocol;protocol = Protocols.HTTP;protocol = Protocols.HTTPS;protocol = Protocols.FTP; // error

转载于:https://www.cnblogs.com/Answer1215/p/9676021.html

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