javascript/ 添加 function 到 repl.it 中的原型

Question

I am following this tutorial .

function Bear(type){
  this.type = type;
}

Bear.prototype.growl = function(){
  console.log('grrr')
}

var grizzly = new Bear('grizzly')
var bBear = new Bear('bBear')

console.log(grizzly, bBear, Bear.growl)

the result of this sould be:

{
  "type": "grizzly",
  "growl": function(){
  console.log('grrr')
}
} {
  "type": "bBear",
  "growl": function(){
  console.log('grrr')
}
} undefined

but what I get in repl.it is:

Bear { type: 'grizzly' } Bear { type: 'bBear' } 

If I put the same code in a SO code snippet, the result is correct.

Why do I get different results here?

Answer 1

This is an artifact of how different environments log objects. On Stack Overflow, Stack Snippets log enumerable properties anywhere on the prototype chain on the object:

 const theProto = { protoProp: 'val' }; const theInstance = Object.create(theProto); theInstance.instanceProp = 'val'; console.log(theInstance);

The same code in Node only logs the properties directly on the object :

{ instanceProp: 'val' }

And repl.it runs the code through Node.

Similarly, with your snippet, since the growl property is on the prototype object, when you log bBear , you'll see growl in a Stack Snippet, but not if you run the same code in Node.

The actual object in Javascript is the same regardless of your environment - you're not doing anything wrong.

Logging behavior is not standardized. It's engine-dependant.