Why output is different in "()=>{}" and "function () {}" function

Question

I thought the output would be same in ()=>{} and function(){} but I got a different output.

1. With function(){}

   var person = {};
   person.name = 'egoing';
   person.introduce = function(){
   return 'My name is '+this.name;
   }
   document.write(person.introduce());
   

the output was

'My name is egoing'

2. But with ()=>{} function,

   var person = {};
   person.name = 'egoing';
   person.introduce = person.introduce=()=>{
   return 'My name is ' +this.name}
   document.write(person.introduce());
   

output was

'My name is '

Why is it differnt??