How does variable declaration differ between the `class` and `constructor`?

Question

I have seen an example, and I am trying to reproduce it. The name and age are declared inside the class and services ( In

Answer 1

in this case

export class Component1 {

      constructor ( 
        private _commonService : CommonService, 
        private _commonServiceIndipendent:commonServiceIndipendent) {


       }

is similar to this

export class Component1 {

      private _commonService : CommonService;
      private _commonServiceIndipendent:commonServiceIndipendent;

      constructor ( 
        _commonService : CommonService, 
        _commonServiceIndipendent:commonServiceIndipendent) {

        this._commonService = _commonService; 
        this._commonServiceIndipendent = _commonServiceIndipendent;

       }

if you do not use in the constructor protected, private, or public, for example, DI, the range of the variable _commonService is the scope of the constructor { } you could not use from another function.

for example:

export class Component1 {

      constructor ( 
        _commonService : CommonService, 
        _commonServiceIndipendent:commonServiceIndipendent) {

          _commonService .... Work
       }

       foo(){

        _commonService ..... Cannot find name '_commonService'.
        this._commonService ..... Property '_commonService' does not exist on type 'yourClass'.  

       }

If you not assign it to another variable that has the scope of the class,so you no could refer to this variable, with this keyword.

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export class Component1 {

  name:string; //why here?
  age:number; //why here?

//can't i add to constructor? if so how?

in typescript without Angular2, you can do this with nothing more:

constructor (name:string, age:number) {}

but in typescript with Angular2, Angular2 is responsible, most of the time, to make use of DI for exaple here:

constructor (private _commonServiceIndipendent:commonServiceIndipendent){}

you use for that providers:[commonServiceIndipendent].

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