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JavaScript: List the properties of a JavaScript object

JavaScript Object: Exercise-1 with Solution

Write a JavaScript program to list the properties of a JavaScript object.
Sample object:
var student = {
name : "David Rayy",
sclass : "VI",
rollno : 12 };
Sample Output: name,sclass,rollno

Sample Solution: -

HTML Code:

<!DOCTYPE html>
  <html>
  <head>
  <meta charset="utf-8">
  <title>JavaScript program to list the properties of a JavaScript object. </title>
  </head>
  <body>
</body>
  </html>

JavaScript Code:

function _keys(obj) 
 {
    if (!isObject(obj)) return [];
    if (Object.keys) return Object.keys(obj);
    var keys = [];
    for (var key in obj) if (_.has(obj, key)) keys.push(key);
    return keys;
  }
function isObject(obj) 
{
    var type = typeof obj;
    return type === 'function' || type === 'object' && !!obj;
  }
console.log(_keys({red: "#FF0000", green: "#00FF00", white: "#FFFFFF"}));

Sample Output:

["red","green","white"]

Flowchart:

Flowchart: JavaScript - List the properties of a JavaScript object.

Live Demo:

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


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Previous: javascript Object Eexercises.
Next: Write a JavaScript program to delete the rollno property from the following object. Also print the object before or after deleting the property.

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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];

console.log(array);

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

// array = [2, 9]
console.log(array);

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 {
      ++i;
    }
  }
  return arr;
}
//Usage
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