get and set in TypeScript

Question

I m trying to create get and set method for a property   private  name  string   Name         get                return this  name            set                this  name                  What s the keyword to set a value

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You can write this  class Human       private firstName   string      private lastName   string       constructor           public FirstName  string           public LastName  string                get FirstName     string           console log  Get FirstName      this firstName           return this firstName            set FirstName value   string            console log  Set FirstName      value           this firstName   value              get LastName     string           console log  Get LastName      this lastName           return this lastName            set LastName value   string            console log  Set LastName      value           this lastName   value

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TypeScript uses getter setter syntax that is like ActionScript3     class foo       private  bar  boolean   false      get bar    boolean           return this  bar            set bar value  boolean            this  bar   value            That will produce this JavaScript  using the ECMAScript 5 Object defineProperty   feature   var foo    function          function foo             this  bar   false            Object defineProperty foo prototype   bar             get  function                  return this  bar                     set  function  value                this  bar   value                     enumerable  true          configurable  true             return foo          So to use it   var myFoo   new foo    if myFoo bar               calls the getter     myFoo bar   false      calls the setter and passes false     However  in order to use it at all  you must make sure the TypeScript compiler targets ECMAScript5   If you are running the command line compiler  use --target flag like this   tsc --target ES5   If you are using Visual Studio  you must edit your project file to add the flag to the configuration for the TypeScriptCompile build tool   You can see that here   As  DanFromGermany suggests below  if your are simply reading and writing a local property like foo bar   true  then having a setter and getter pair is overkill   You can always add them later if you need to do something  like logging  whenever the property is read or written

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It is very similar to creating common methods  simply put the keyword reserved get or set at the beginning     class Name      private  name  string       getMethod    string          return this  name             setMethod value  string           this  name   value            get getMethod1    string          return this  name             set setMethod1 value  string           this  name   value          class HelloWorld        public static main             let test   new Name             test setMethod  test getMethod   --- need                   console log test getMethod              test setMethod1    test getMethod1 --- no need     and used   for set                console log test getMethod1           HelloWorld main        In this case you can skip return type in get getMethod1           get getMethod1             return this  name

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Ezward has already provided a good answer  but I noticed that one of the comments asks how it is used  For people like me who stumble across this question  I thought it would be useful to have a link to the official documentation on getters and setters on the Typescript website as that explains it well  will hopefully always stay up-to-date as changes are made  and shows example usage   http   www typescriptlang org docs handbook classes html  In particular  for those not familiar with it  note that you don t incorporate the word  get  into a call to a getter  and similarly for setters     var myBar   myFoo getBar       wrong     var myBar   myFoo get  bar        wrong   You should simply do this   var myBar   myFoo bar      correct  get  myFoo bar   true      correct  set   false is correct too obviously     given a class like   class foo     private  bar boolean   false     get bar   boolean       return this  bar        set bar theBar boolean        this  bar   theBar          then the  bar  getter for the private   bar  property will be called

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TS offers getters and setters which allow object properties to have more control of how they are accessed  getter  or updated  setter  outside of the object  Instead of directly accessing or updating the property a proxy function is called   Example   class Person       constructor name  string            this  name   name             private  name  string       get name             return this  name                first checks the length of the name and then updates the name      set name name  string            if  name length  gt  10                throw new Error  Name has a max length of 10                       this  name   name               doStuff              this  name    foofooooooofoooo              const person   new Person  Willem        doesn t throw error  setter function not called within the object method when this  name is changed person doStuff          throws error because setter is called and name is longer than 10 characters person name    barbarbarbarbarbar

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If you are looking for way to use get and set on any object  not a class  Proxy  may be usefull  https   developer mozilla org en-US docs Web JavaScript Reference Global Objects Proxy  const target       message1   hello     message2   everyone      const handler3       get  function  target  prop  receiver        if  prop      message2           return  world             return Reflect get    arguments            const proxy3   new Proxy target  handler3    console log proxy3 message1      hello console log proxy3 message2      world   Note  be aware that this is new api not supported and required polifill for older browsers

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If you are working with TypeScript modules and are trying to add a getter that is exported  you can do something like this        dataStore ts export const myData  string   undefined      just for typing support let  myData  string      for memoizing the getter results  Object defineProperty this   myData         get      string   gt            if   myData     undefined                 myData    my data       pretend this took a long time                    return  myData               Then  in another file you have   import   as dataStore from    dataStore  console log dataStore myData       my data

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Here s a working example that should point you in the right direction   class Foo        name       get Name             return this  name             set Name val            this  name   val            Getters and setters in JavaScript are just normal functions  The setter is a function that takes a parameter whose value is the value being set

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I think I probably get why is it so confusing  In your example  we wanted getters and setters for  name  But we achieve that by creating getters and setters for an unrelated class variable Name   Consider this   class Car      private tiresCount   4      get yourCarTiresCount            return this tiresCount             set yourCarTiresCount count            alert  You shouldn t change car tire count             Above code does following    get and set create getter and setter for yourCarTiresCount  not for tiresCount     The getter is    function         return this tiresCount       and the setter is    function count        alert  You shouldn t change car tire count        Meaning  every time we do new Car   yourCarTiresCount  getter runs  And for every new Car   yourCarTiresCount  7   setter runs    Indirectly create getter  but not the setter  for private tireCount

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Based on example you show  you want to pass a data object and get a property of that object by get    for this you need to use generic type  since data object is generic  can be any object  export class Attributes lt T gt        constructor private data  T         get    lt K extends keyof T gt  key  K   T K    gt          return this data key              set    update  T   void   gt               this is like spread operator  it will take this data obj and will overwrite with the update obj          ins tsconfig json change target to Es6 to be able to use Object assign         Object assign this data  update              getAll    T         return this data              lt  T  gt  refers to generic type  let s initialize an instance  const myAttributes new Attributes  name  quot something quot  age 32     myAttributes get  quot name quot    quot something quot   Notice this syntax  lt K extends keyof T gt   in order to be able to use this we should be aware of 2 things  1- in typestring strings can be a type  2- all object properties in javascript essentially are strings  when we use get    type of argument that it is receiving is a property of object that passed to constructor and since object properties are strings and strings are allowed to be a type in typescript  we could use this   lt K extends keyof T gt

[typescript] get and set in TypeScript

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