title: How to avoid the original variable being reset in this js date sum
body: <p>I have this simple javascript function to sum a date</p>
  
  <pre><code>    console.log(this.state.birth_date)  //logs birth date
  
      var death_date = this.state.birth_date.setFullYear(this.state.birth_date.getFullYear() + this.state.years_to_live) 
  
      console.log(this.state.birth_date) //logs death date
      console.log(death_date) //logs death date
  </code></pre>
  
  <p>How to avoid the birth date being set as death date after the  death date is set?</p>