Loop through an Object is much harder than doing the same thing in an Array because you can’t use those convenient syntaxes like for-of, forEach (by the way, you should never use for-in) when dealing with an Object, so today let’s look at how many methods are there to loop through an Object

Create an object to test

function Ob() {
  this.name = "liu";
  this.age = 22;
}
var ob = new Ob();

Object.defineProperty(ob, "gender", {
  value: "male",
  enumerable: false,
});

var mySb = Symbol("special");

ob[mySb] = "sp";

var mySbEnumerableFalse = Symbol("emfalse");
Object.defineProperty(ob, mySbEnumerableFalse, {
  value: "emfalse:value",
  enumerable: false,
});

Ob.prototype.father = "leo";

console log this in Node:

console.log(ob);

output:
Ob { name: 'liu', age: 22, [Symbol(special)]: 'sp' }

notice,console.log(Object) will only output own enumerable properties.

Object.keys(Object)(Object.Values(); Object.entries())

those methods above will return an array including the parameter Object’s keys or values or [key, value] pairs, here’s the code:

console.log(Object.values(object)); // ignore enumerable: false 
console.log(Object.keys(object)); // ignore enumerable: false 
console.log(Object.entries(object)); // ignore same

output here:

[ 'liu', 22 ] // Object.values(object)
[ 'name', 'age' ] // Object.keys(object)
[ [ 'name', 'liu' ], [ 'age', 22 ] ] // Object.entries(object)

so these three methods only count their own enumerable none symbol properties in

Object.getOwnPropertyNames（getOwnPropertySymbols(ob)）

directly look at the code:

console.log(Object.getOwnPropertyNames(ob)); // enumerable: false would still in output array [names....], but no symbol keys
console.log(Object.getOwnPropertySymbols(ob)); // enumerable: false would still in output array [names....], only symbol keys

output:

[ 'name', 'age', 'gender' ]
[ Symbol(special), Symbol(emfalse) ]

The two are complementary, and will output all own properties but not include ancestors’, no matter how the enumerable.

Reflect.ownKeys()

it’s do the same thing as Object.getOwnPropertyNames() and Object.getOwnPropertySymbols(ob)
code here:

console.log(Reflect.ownKeys(ob));

output:
[ 'name', 'age', 'gender', Symbol(special), Symbol(emfalse) ]

summary

which methods to use it’s a subjective topic, it’s up to your real code context, and I like the use Reflect.ownKeys() , but it’s only available in es6, so i will contact Object.getOwnPropertyNames() and Object.getOwnPropertySymbols(ob)

Reference List

JS遍历对象的七种方法