Default array value to class constructor angular 2

Question

class DateComponent {
  constructor(public months:string[] = [],public days:number[] = [] , public years:number[] = []) { }

};

This is giving me error in Chrome. Says "=" is invalid. I am using angular 2 and typescript and webpack dev server.

How can i pass values to the parameters in constructor?

Answer 1

Like Harry says in the comment, defining class members in the constructor is reserved for dependency injection in Angular 2.

I'd suggest moving those out of the constructor:

class DateComponent {
  public months: Array<string> = [];
  public days: Array<string> = [];
  public years: Array<string> = [];

  constructor() { 

  }
}

Answer 2

if you want optional parameter of constructor you must add "?". But the parameter of the object must define out of constructor.

In angular2 u will see that some parameter define in constructor but this have use in annotation (@Component, @Directive,...) that's define there as class property.

if i understand correct you want something like this:

class DateComponent {
      public months: [] = [];
      public days: [] = [];
      public years: [] = [];

      constructor(_months?:string[],_days?:number[], _years?:number[]) {
       this.months = _months;
       this.days = _days;
       this.years = _years;
     }

    };