current position:Home>TS (typescript) basics 6: (literal) text type
TS (typescript) basics 6: (literal) text type
2021-08-27 10:10:54 【HealthyZhang】
This is my participation 8 The fourth of the yuegengwen challenge 11 God , Check out the activity details :8 Yuegengwen challenge
Literal type
This chapter introduces a TS Special types in Literal( In addition to general types of strings and numbers , We can also refer to specific strings and numbers at type locations ) In order to achieve some wonderful effects .
Constant
Let's look at an example : Use literal types to implement constant like functions . Take this example to understand its basic operation mechanism .
let s: 'hw' = 'hw'
let n: 1 = 1;
Copy code
In the above example : Statement s The value of is string ‘hw';n The value of is 1; You can't change it later .
But having a variable with only one value is not very useful , Use const Can be easily implemented
Joint type
We can combine words into joint types , Can express a more useful concept
for example , Functions that accept only a specific set of known values
type a = -1 | 0 | 1
function compare(a: string, b: string): a {
return a === b ? 0 : a > b ? 1 : -1;
}
Copy code
In the above example, suppose we need a version comparison method compare, The return value only accepts 0,1,-1 Three values .
Combined interface
We can also use it with interfaces :
interface f {
age: number;
}
type s = f | 'son'
function fn(x: s) { }
fn({ age: 100 });
fn("son");
Copy code
In the above example , Alias s Both interfaces f The rules of .
There is also a special type of text : Boolean type . Boolean types have only two Boolean text types , The difference is true and false type . This shows that the type boolean Itself is actually just a union type in a text type
application
Here's an example , Show the application in the actual project
We declare one http Request method , And call it , See the following example :
type obj = {
url: string;
method: "GET" | "POST"
}
function http(arg: obj) { }
let params = { url: 'www.lsdj.sdf', method: "GET" }
http(params)
Copy code
//Type 'string' is not assignable to type '"GET" | "POST"'.
analysis :
The variables we declare params in method The value of is a string type , therefore TS Help me method Inferred as string type . But our encapsulated request method http Only text types are accepted in "GET" | "POST"! If you want this code to work properly, you need to change params in method The type of
let params = { url: 'www.lsdj.sdf', method: "GET" as "GET" }
let params = { url: 'www.lsdj.sdf', method: "GET" } as const
Copy code
The above two ways , Can meet our needs
Object constant
except readonly Outside the modifier , Other ways to make the value in the object immutable
let obj = { a: 1} as const;
Copy code
as const The function of suffix is similar to const, But for type systems , Make sure that all attributes are assigned to the text type , Not a more general version , Such as string or number .
copyright notice
author[HealthyZhang],Please bring the original link to reprint, thank you.
https://en.qdmana.com/2021/08/20210827101050516l.html
The sidebar is recommended
- Crazy blessing! Tencent boss's "million JVM learning notes", real topic of Huawei Java interview 2020-2021
- JS JavaScript how to get the subscript of a value in the array
- How to implement injection in vuex source code?
- JQuery operation select (value, setting, selected)
- One line of code teaches you how to advertise on Tanabata Valentine's Day - Animation 3D photo album (music + text) HTML + CSS + JavaScript
- An article disassembles the pyramid architecture behind the gamefi outbreak
- BEM - a front-end CSS naming methodology
- [vue3] encapsulate custom global plug-ins
- Error using swiper plug-in in Vue
- Another ruthless character fell by 40000, which was "more beautiful" than Passat and maiteng, and didn't lose BMW
guess what you like
-
Huang Lei basks in Zhang Yixing's album, and the relationship between teachers and apprentices is no less than that in the past. Netizens envy Huang Lei
-
He was cheated by Wang Xiaofei and Li Chengxuan successively. Is an Yixuan a blessed daughter and not a blessed home?
-
Zhou Shen sang the theme song of the film "summer friends and sunny days" in mainland China. Netizen: endless aftertaste
-
Pink is Wangyuan online! Back to the peak! The new hairstyle is creamy and sassy
-
Front end interview daily 3 + 1 - day 858
-
Spring Webflux tutorial: how to build reactive web applications
-
[golang] walk into go language lesson 24 TCP high-level operation
-
August 23, 2021 Daily: less than three years after its establishment, Google dissolved the health department
-
The female doctor of Southeast University is no less beautiful than the female star. She has been married four times, and her personal experience has been controversial
-
There are many potential safety hazards in Chinese restaurant. The top of the program recording shed collapses, and the artist will fall down if he is careless
Random recommended
- Anti Mafia storm: He Yun's helpless son, Sun Xing, is destined to be caught by his dry son
- Introduction to flex flexible layout in CSS -- learning notes
- CSS learning notes - Flex layout (Ruan Yifeng tutorial summary)
- Today, let's talk about the arrow function of ES6
- Some thoughts on small program development
- Talk about mobile terminal adaptation
- Unwilling to cooperate with Wang Yibo again, Zhao Liying's fans went on a collective strike and made a public apology in less than a day
- JS function scope, closure, let, const
- Zheng Shuang's 30th birthday is deserted. Chen Jia has been sending blessings for ten years. Is it really just forgetting to make friends?
- Unveil the mystery of ascension
- Asynchronous solution async await
- Analysis and expansion of Vue infinite scroll source code
- Compression webpack plugin first screen loading optimization
- Specific usage of vue3 video play plug-in
- "The story of huiyeji" -- people are always greedy, and fairies should be spotless!
- Installing Vue devtool for chrome and Firefox
- Basic usage of JS object
- 1. JavaScript variable promotion mechanism
- Two easy-to-use animation JS that make the page move
- Front end Engineering - scaffold
- Java SQL Server intelligent fixed asset management, back end + front end + mobile end
- Mediator pattern of JavaScript Design Pattern
- Array de duplication problem solution - Nan recognition problem
- New choice for app development: building mobile applications using Vue native
- New gs8 Chengdu auto show announces interior Toyota technology blessing
- Vieira officially terminated his contract and left the team. The national security club sent blessings to him
- Less than 200000 to buy a Ford RV? 2.0T gasoline / diesel power, horizontal bed / longitudinal bed layout can be selected
- How does "heart 4" come to an end? Pinhole was boycotted by the brand, Ma Dong deleted the bad comments, and no one blessed him
- We are fearless in epidemic prevention and control -- pay tribute to the front-line workers of epidemic prevention!
- Front end, netty framework tutorial
- Xiaomi 11 | miui12.5 | android11 solves the problem that the httpcanary certificate cannot be installed
- The wireless charging of SAIC Roewe rx5 plus is so easy to use!
- Upload and preview pictures with JavaScript, and summarize the most complete mybatis core configuration file
- [25] typescript
- CSS transform Complete Guide (Second Edition) flight.archives 007
- Ajax foundation - HTTP foundation of interview essential knowledge
- Cloud lesson | explain in detail how Huawei cloud exclusive load balancing charges
- Decorator pattern of JavaScript Design Pattern
- [JS] 10. Closure application (loop processing)
- Left hand IRR, right hand NPV, master the password of getting rich