current position:Home>Why can typescript fight side by side with JavaScript (2) - practical methods for typescript type conversion (Part 1)
Why can typescript fight side by side with JavaScript (2) - practical methods for typescript type conversion (Part 1)
2021-08-27 04:47:35 【zidea】
This is my participation 8 The fourth of the yuegengwen challenge 23 God , Check out the activity details :8 Yuegengwen challenge
TypeScript Several utility types are provided , Transform the original type to get a new type , A bit like a specific function , Receive one or more types as input , Output a new type .
Feeling Typescript Provide depth , And you can understand JavaScript On the basis of , Understand from simple to deep TypeScript
Everyone may think that JavaScript
Too simple , Closure 、 Prototype chains and higher-order functions play , No difficulty. , Not fun enough . There is now a TypeScript, It can meet your requirements . Maybe I'm superficial , But for the time being, I saw some Typescript , I feel that some contents are really incomprehensible , Probably JavaScript You're too familiar with me . Complex design does not mean reasonable , Let's take a look TypeScript Provide us with this set Type Whether the solution is feasible and effective , Is it designed for some pain points of large-scale development .
Type Practical methods
stay TypeScript Provide a variety of methods to operate on types , Or it can be said to be a method of converting types . Provide a new type through operation based on the existing type .
Partial<Type>
Create a type based on an existing type , Set all properties of the original type to optional . It can also be understood as the type of all subsets of existing types , Explain with an example to help you understand .
interface Tut{
title:string;
content:string;
}
const updateTut = (tut:Tut,updatedTut:Tut)=>{
return {...tut,...updatedTut}
}
const tut_1:Tut = {
title : "machine learning",
content : "machine learning content",
}
const update_tut:Tut = {
title:"update machine learning",
content:"update machine leanring content"
}
const updated_tut = updateTut(tut_1,update_tut)
console.log(updated_tut)
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The above code we use interface
Interface defined Tut
, Can be of type , Next, define a function updateTut
Takes two Tut
Parameters of type , All the function has to do is update the first parameter with the second parameter . Because if both parameter types are interfaces Tut
Then each parameter needs to implement all the properties and methods of the interface .
{
title: 'update machine learning',
content: 'update machine leanring content'
}
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If we just want to use the second 2 Parameter a property to update the first parameter , But because they all need to be Tut
type , The interface has certain constraints , You need to implement the interface or interface type variables. You need to implement the interface definition properties , And then you can use this Partial<Type>
,Partial<Type>
Type indicates the second 2 Parameters can only implement interfaces Tut Part of the , Just give the attribute to be updated .
const updateTut = (tut:Tut,updatedTut:Partial<Tut>)=>{
return {...tut,...updatedTut}
}
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here ...
Deconstruction symbol , In this way, you can use updatedTut
To update tut
const updated_tut = updateTut(tut_1,{
content:"update machine leanring content"
})
console.log(updated_tut)
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{
title: 'machine learning',
content: 'update machine leanring content'
}
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Required<Type>
It's described above Partial
It can be said to be strict before payment , But the opposite operation is this Required
This is a wide first and then strict operation . The situation is that when defining an interface , The properties and methods of the interface are optional . In fact, sometimes I feel TypeScript There are many ways to implement the same function , Sometimes you need to let go , Sometimes you have to be more rigorous , For type control, it is a relaxation , Provides control over type richness .
interface Article{
title?:string;
text?:string;
}
const machine_learning_article:Article = {title:"machine leanring"}
// Property 'text' is missing in type '{ title: string; }' but required in type 'Required<Article>'.ts(2741)
// demo_02.ts(3, 5): 'text' is declared here.
const deep_learning_article:Required<Article> = {title:"deep learning",text:"deep learning"}
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Readonly<Type>
Use Readonly<Type>
When converting a type , It can be found that once the type attribute is assigned , You can't change .
const machine_learning_article:Readonly<Article> = {title:"machine leanring"}
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// Cannot assign to 'title' because it is a read-only property.ts(2540)
machine_learning_article.title = "updated machine learning"
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Constructs an object type whose property keys are Keys and whose property values are Type. This utility can be used to map the properties of a type to another type.
Define an object type , Its attribute key type is Keys
, Its attribute value type is Type
. This tool can be used to map properties of one type to another .
interface TutInfo{
title:string;
lesson:number;
}
type TutCategoryName = "programming" | "machineleanring" | "codetools"
const tuts: Record<TutCategoryName, TutInfo> = {
programming:{title:"basic python programming", lesson:12},
machineleanring:{title:"basic python programming", lesson:12},
codetools:{title:"basic python programming", lesson:12},
}
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Pick<Type, Keys>
Pick
Type is to select several properties on an existing type to get a new type , This new type is a subset of the existing type . This operation is similar to starting from a qualifier .
interface Tut{
title:string;
lesson:number;
completed:boolean;
description:string;
}
type TutPreview = Pick<Tut, "title" | "description" | "completed" >;
const tut:TutPreview = {
title:"machine learning",
description:"machine leanring",
completed:false,
}
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Omit<Type, Keys>
This operation can be understood as ·Pick
The inverse operation , That is to exclude... From existing types Keys Get a new type .
type TutPreview2 = Omit<Tut, "lesson">;
const tut2:TutPreview2 = {
title:"deep learning",
description:"deep leanring",
completed:false,
}
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Record<Keys,Type>
Keys Is the key value ,Type Is the type corresponding to the key value .
const rec:Record<string,number> = {
machineLearningTut:12,
deepLearningTut:16,
}
const tuts: Record<string,Tut> ={
MachineLearningTut:{
title:"machine learning tut",
isCompleted:true
},
DeeplearningTut:{
title:"deep leanring tut",
isCompleted:false
}
}
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