jsはA関数を実現してB関数を継承します.

function A(){
     
	this.name = '  '
}

function B(name){
     
	this.eat = function(){
     
		console.log('  b  eat')
	}
}

//   a    b  
A.prototype = new B()		

new A().eat()

function A(){
     
	B.call(this)
	this.name = '  '
}

function B(){
     
	this.eat = function(){
     
		console.log('  b  eat')
	}
}		

new A().eat()