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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

instance

class Calc {
	constructor() {
		this.count = 0 
	}

	increase() {
		this.count ++
	}
}

const calc = new Calc()
new Calc().increase()

console.log(calc.count)

We set the variable calc equal to a new instance of the Calc class. Then, we instantiate a new instance of Calc, and invoke the increase method on this instance. Since the count property is within the constructor of the Calc class, the count property is not shared on the prototype of Calc. This means that the value of count has not been updated for the instance calc points to, count is still 0.

Ref: https://bit.ly/2Hcpkm6