为什么console.log显示不同的描述

Question

I run the following in node: why does the first console.log show:

greet: [Function],

and the second console.log show:

greet: [Function: greet]

Is there any difference? (note, console.log in chrome doesn't show the difference)

 function deepCopy(obj){ /* an object has key value pairs check if val is object if true deepCopy(val) else return value */ const keys = Object.keys(obj); // gets keys of object const newObject = {} for(index in keys){ if(typeof(obj[keys[index]]) === 'object') { newObject[keys[index]] = deepCopy(obj[keys[index]]) }else{ newObject[keys[index]] = obj[keys[index]] } } return newObject } o={ name:'David', teach:true, obj:{ greet:function(){ console.log('hi!')}, last:'cross' } } o2 = deepCopy(o) o.obj.greet=function(){ console.log('bye')} o.name='george' console.log(o) console.log(o2) o.obj.greet() o2.obj.greet() 

Answer 1

1. When you declare the method { great:function(){} } , it will have a .name and will be print out by console.log . Even you pass it around (assign to o2 via deepCopy ), it will keep it name.
2. When you create an anonymous function function(){} , it's .name is empty. which you assign it to o.great = function(){} .

I create a simplify version to explain op question to test.

 const a = { great: function(){} }; // in object declaration, method great as name "great" (x) const b = {}; b.great = function(){}; // b.great is point to an anonymous function with no name (y) // When console.log a function, if function has name, it will show out console.log("a.great", a.great); console.log("b.great", b.great); console.log("a.great.name", JSON.stringify(a.great.name)); // "great" console.log("b.great.name", JSON.stringify(b.great.name)); // ""; b.great = a.great; // simliar when you deep copy o2 from o // in this case, b.great is point to the method great (x) // so when you log out the name, it will print out console.log("b.great.name", JSON.stringify(b.great.name)); // "great" a.great = function(){}; // similar when o.great get re-assign // a.great got re-assign to an anonymous function with no name (z) // so when you log out the name, it will print out "" console.log("a.great.name", JSON.stringify(a.great.name)); // "" // Finally: console.log(a.great); console.log(b.great);