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Difference between private keyword and private fields in TypeScript. The Complete TypeScript Developer Course 2022 [Videos].

TypeScript 3.8 supports the private keyword to declare its members private. And the private fields in TypeScript are the ones newly proposed for JavaScript. These fields are preceded by #.

Private keyword: The private keyword in TypeScript is used to mark a member private which makes it inaccessible outside the declared class. The fields are preceded by the private keyword to mark them private.

  • Syntax:
    private variableName
  • Example:

    class letters { 
        private a;
      
        constructor(alphabet){ 
            this.a = alphabet;
        
     
        getA(){
            return this.a;
        }
    const l = new letters("gfg"); 
    console.log(l.getA()); 
  • Output:
    gfg

Private fields: Private fields in TypeScript are the ones that have been newly added to JavaScript, the members to be declared private are preceded by a #. Private members cannot be accessed outside their class.

  • Syntax:
    #variableName
  • Example:

    class letters {
        #a;
     
        constructor(alphabet){
            this.#a = alphabet;
        }
     
        getA(){
            return this.#a;
        }
    }
    const l = new letters("gfg");
    console.log(l.getA());            

    Output:

  • gfg

Hence, to implement the private keyword in runtime when compiling TypeScript to ESNext JavaScript one must consider using the private syntax # defined for JavaScript.

Difference between private keyword and private fields:

Private keywordPrivate fields
It is a TypeScript modifier.It is a newly added syntax by ECMA to JavaScript, which is also available in TypeScript.
It is a compile time annotation. So, when a transpiler converts TypeScript code to JavaScript, the private keyword is removed.The private fields remain private at runtime even after the TypeScript code gets converted to JavaScript by the transpiler.

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