javascript why calling a method from another method in the same class need this?

Question

JavaScript code below.

class Test{
    testMethod1() {
      console.log('hello world');
    }
    testMethod2() {
      this.testMethod1();
    }
}
let t = new Test();
t.testMethod1();
t.testMethod2();

I already know that when calling a method from another method in the same class needs a this pointer. But why JavaScript need this? Seems that cpp, java and othter object oriented langauge do not need this.

Answer 1

this in this context means you refer to the current object which is just instantiated by new. Without this, the compiler will understand that you refer to an outer-scoped function.

function testMethod1() {
   console.log('outer world');
}

class Test{
    testMethod1() {
      console.log('hello world');
    }
    testMethod2() {
      testMethod1(); //removed `this`
    }
}

let t = new Test();
t.testMethod1(); //hellow world
t.testMethod2(); //outer world

I'm not sure where you are pointing out that Java or other object-oriented programming languages do not need this. You can try this playground for Java.