JavaScript Object.keys()

JavaScript Object.keys()
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The Object.keys() method returns an array of a given object’s own enumerable properties, in the same order as that provided by a for...in loop (the difference being that a for-in loop enumerates properties in the prototype chain as well).

Syntax

Object.keys(obj)

Parameters

obj

The object whose enumerable own properties are to be returned.

MDN link | MSDN link

Description

Object.keys() returns an array whose elements are strings corresponding to the enumerable properties found directly upon object. The ordering of the properties is the same as that given by looping over the properties of the object manually.

Examples

var arr = ['a', 'b', 'c'];
console.log(Object.keys(arr)); // console: ['0', '1', '2']

// array like object
var obj = { 0: 'a', 1: 'b', 2: 'c' };
console.log(Object.keys(obj)); // console: ['0', '1', '2']

// array like object with random key ordering
var an_obj = { 100: 'a', 2: 'b', 7: 'c' };
console.log(Object.keys(an_obj)); // console: ['2', '7', '100']

// getFoo is property which isn't enumerable
var my_obj = Object.create({}, { getFoo: { value: function() { return this.foo; } } });
my_obj.foo = 1;

console.log(Object.keys(my_obj)); // console: ['foo']
// Create a constructor function.
function Pasta(grain, width, shape) {
    this.grain = grain;
    this.width = width;
    this.shape = shape;

    // Define a method.
    this.toString = function () {
        return (this.grain + ", " + this.width + ", " + this.shape);
    }
}

// Create an object.
var spaghetti = new Pasta("wheat", 0.2, "circle");

// Put the enumerable properties and methods of the object in an array.
var arr = Object.keys(spaghetti);
document.write (arr);

// Output:
// grain,width,shape,toString