JavaScript: Iterate over all own properties of an object, running a callback for each one

JavaScript fundamental (ES6 Syntax): Exercise-77 with Solution

Write a JavaScript program to iterate over all own properties of an object, running a callback for each one.

  • Use Object.keys(obj) to get all the properties of the object.
  • Use Array.prototype.forEach() to run the provided function for each key-value pair.
  • The callback receives three arguments - the value, the key and the object.

Sample Solution:

JavaScript Code:

//#Source https://bit.ly/2neWfJ2 
const forOwn = (obj, fn) => Object.keys(obj).forEach(key => fn(obj[key], key, obj));
forOwn({ foo: 'bar', a: 1 }, v => console.log(v)); // 'bar', 1

Sample Output:



flowchart: Iterate over all own properties of an object, running a callback for each one

Live Demo:

See the Pen javascript-basic-exercise-76-1 by w3resource (@w3resource) on CodePen.

Improve this sample solution and post your code through Disqus

Previous: Write a JavaScript program to execute a provided function once for each array element, starting from the array's last element.
Next: Write a JavaScript program to invert the key-value pairs of an object, without mutating it. The corresponding inverted value of each inverted key is an array of keys responsible for generating the inverted value. If a function is supplied, it is applied to each inverted key.

What is the difficulty level of this exercise?

Test your Programming skills with w3resource's quiz.

JavaScript: Tips of the Day

How to remove a specific item from an array?

Find the index of the array element you want to remove using indexOf, and then remove that index with splice.

The splice() method changes the contents of an array by removing existing elements and/or adding new elements.

const array = [2, 5, 9];


const index = array.indexOf(5);
if (index > -1) {
  array.splice(index, 1);

// array = [2, 9]

The second parameter of splice is the number of elements to remove. Note that splice modifies the array in place and returns a new array containing the elements that have been removed.

For the reason of completeness, here are functions. The first function removes only a single occurrence (i.e. removing the first match of 5 from [2,5,9,1,5,8,5]), while the second function removes all occurrences:

function removeItemOnce(arr, value) {
  var index = arr.indexOf(value);
  if (index > -1) {
    arr.splice(index, 1);
  return arr;

function removeItemAll(arr, value) {
  var i = 0;
  while (i < arr.length) {
    if (arr[i] === value) {
      arr.splice(i, 1);
    } else {
  return arr;
console.log(removeItemOnce([2,5,9,1,5,8,5], 5))
console.log(removeItemAll([2,5,9,1,5,8,5], 5))

Ref: https://bit.ly/2N9nKRp