Question

我在节点中运行以下命令：为什么第一个console.log显示：

greet: [Function],

和第二个console.log显示：

greet: [Function: greet]

有什么区别吗？（注意，chrome中的console.log没有显示差异）

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

当您声明方法{ great:function(){} }时，它将有一个.name，并将由console.log打印出来。即使你传递它（通过o2分配给deepCopy），也会保留它的名称。
当您创建匿名函数function(){}时，它的.name为空。您将其分配给o.great = function(){}。

我创建了一个简化版本来解释运行问题以进行测试。

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);

为什么console.log显示不同的描述

1 个答案: