Object.getOwnPropertyNames

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JS Concepts

JS Language Reference

Object.getOwnPropertyNames()

The Object.getOwnPropertyNames() method returns an array of all properties (enumerable or not) found directly upon a given object.

Syntax

Object.getOwnPropertyNames(obj)

Parameters

obj

The object whose enumerable and non-enumerable own properties are to be returned.

MDN link | MSDN link

Description

Object.getOwnPropertyNames() returns an array whose elements are strings corresponding to the enumerable and non-enumerable properties found directly upon object. The ordering of the enumerable properties in the array is consistent with the ordering exposed by a for...in loop (or by Object.keys()) over the properties of the object. The ordering of the non-enumerable properties in the array, and among the enumerable properties, is not defined.

Examples

var arr = ['a', 'b', 'c'];
console.log(Object.getOwnPropertyNames(arr).sort()); // logs '0,1,2,length'

// Array-like object
var obj = { 0: 'a', 1: 'b', 2: 'c' };
console.log(Object.getOwnPropertyNames(obj).sort()); // logs '0,1,2'

// Logging property names and values using Array.forEach
Object.getOwnPropertyNames(obj).forEach(function(val, idx, array) {
  console.log(val + ' -> ' + obj[val]);
});
// logs
// 0 -> a
// 1 -> b
// 2 -> c

// non-enumerable property
var my_obj = Object.create({}, {
  getFoo: {
    value: function() { return this.foo; },
    enumerable: false
  }
});
my_obj.foo = 1;

console.log(Object.getOwnPropertyNames(my_obj).sort()); // logs 'foo,getFoo'

function Pasta(grain, size, shape) {
    this.grain = grain; 
    this.size = size; 
    this.shape = shape; 
}

var spaghetti = new Pasta("wheat", 2, "circle");

var names = Object.getOwnPropertyNames(spaghetti).filter(CheckKey);
document.write(names); 

// Check whether the first character of a string is 's'. 
function CheckKey(value) {
    var firstChar = value.substr(0, 1); 
    if (firstChar.toLowerCase() == 's')
        return true; 
    else
         return false; 
}
// Output:
// size,shape

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