javascript class variable inside function says undefined ES6

Attaching a variable to the class context doesn't happen just by declaring it. You have to be explicit:

class Auto {
  printauto() {
    this.type = "2 wheeler"; // explicitly attach to `this`
    this.color = "green";    // same here
    console.log("Car type is="+this.type+" "+" and color="+this.color);
 }
}

new Auto().printauto();

The constructor is usually the best place for such initialization:

class Auto {
  constructor() {
    this.type = "2 wheeler"; // explicitly attach to `this`
    this.color = "green";    // same here
  }
  printauto() {
    console.log("Car type is="+this.type+" "+" and color="+this.color);
 }
}

new Auto().printauto();

This refer to class and you don't have color and type declared in your class. The color and are scoped inside your printauto method. either you declare them in your class or just do this

console.log("Car type is="+type+" "+" and color="+color);

By declaring in class

class Auto {
    this.type = "2 wheeler";
    this.color = "green";

    printauto() {
        console.log("Car type is=" + this.type + " " + " and color=" + this.color);
    }
}
var a = new Auto();
a.printauto();

As described by Felix King in comment, variable a is not the same as properties of class Auto

class Auto {
  printauto() {
    var type = "2 wheeler";
    var color = "green";
    console.log("Car type is="+ type+" "+" and color="+color);
 }
}

var a = new Auto();
a.printauto();