Object property access doesn't work in ES6 function expression

Question

I can't access my object property with this ES6 expression :

const obj =
{
    name: 'john',
    test: () => console.log('hello'+this.name)
} 
obj.test()

I only get "hello", and with this expression it works :

const obj =
    {
        name: 'john',
        test: function() {
            console.log('hello'+this.name)
        }
}

What's happening here ?