TypeScript singleton types All In One

TypeScript singleton types All In One

单例类型 / 字面量类型

singleton types / literal types

1. enum member types / 枚举成员类型

enum EventName {
    click = 'click',
    scroll = 'scroll',
    mousemove = 'mousemove',
};

function handleEvent(ele: Element, event: EventName) {
    // do something
}

handleEvent(document.getElementById('btn') as HTMLElement, EventName.scroll);

string enums

"use strict";
var EventName;
(function (EventName) {
    EventName["click"] = "click";
    EventName["scroll"] = "scroll";
    EventName["mousemove"] = "mousemove";
})(EventName || (EventName = {}));

https://www.typescriptlang.org/docs/handbook/enums.html#string-enums

enum EventName {
    'click',
    'scroll',
    'mousemove'
};

function handleEvent(ele: Element, event: EventName) {
    // do something
}

handleEvent(document.getElementById('btn') as HTMLElement, EventName.scroll);

numeric enums

"use strict";
var EventName;
(function (EventName) {
    EventName[EventName["click"] = 0] = "click";
    EventName[EventName["scroll"] = 1] = "scroll";
    EventName[EventName["mousemove"] = 2] = "mousemove";
})(EventName || (EventName = {}));

https://www.typescriptlang.org/docs/handbook/enums.html#numeric-enums

2. numeric literal types / 数字字面量类型

type EventName = 1 | 2 | 3;

type Types = {
    1: 'click',
    2: 'scroll',
    3: 'mousemove',
}

function handleEvent(ele: Element, event: Types[EventName]) {
    // do something
}

handleEvent(document.getElementById('btn') as HTMLElement, 'scroll');
// ✅
handleEvent(document.getElementById('btn') as HTMLElement, 'dblclick');
// ❌ Argument of type '"dblclick"' is not assignable to parameter of type '"click" | "scroll" | "mousemove"'.(2345)

3. string literal types / 字符串字面量类型

type EventName = 'click' | 'scroll' | 'mousemove';

function handleEvent(ele: Element, event: EventName) {
    // do something
}

handleEvent(document.getElementById('btn') as HTMLElement, 'scroll');
// ✅
handleEvent(document.getElementById('btn') as HTMLElement, 'dblclick');
// ❌ Argument of type '"dblclick"' is not assignable to parameter of type 'EventName'.(2345)

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Enums at compile time

keyof typeof

enum LogLevel {
  ERROR,
  WARN,
  INFO,
  DEBUG,
}

type LogLevelStrings = keyof typeof LogLevel;
// type LogLevelStrings = 'ERROR' | 'WARN' | 'INFO' | 'DEBUG';

function printImportant(key: LogLevelStrings, message: string) {
  const num = LogLevel[key];
  if (num <= LogLevel.WARN) {
    console.log("Log level key is:", key);
    console.log("Log level value is:", num);
    console.log("Log level message is:", message);
  }
}
printImportant("ERROR", "This is a message");

https://www.typescriptlang.org/docs/handbook/enums.html#enums-at-compile-time

refs

https://www.typescriptlang.org/docs/handbook/enums.html#union-enums-and-enum-member-types

https://www.typescriptlang.org/docs/handbook/advanced-types.html#enum-member-types

https://ts.xcatliu.com/advanced/string-literal-types.html

https://www.cnblogs.com/xgqfrms/tag/Enum

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