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JavaScript: Return true if the specified value is undefined, false otherwise

JavaScript fundamental (ES6 Syntax): Exercise-185 with Solution

Write a JavaScript program that will return true if the specified value is undefined, false otherwise.

Note: Use the strict equality operator to check if the value and of val are equal to undefined.

  • Use the strict equality operator to check if val is equal to undefined.

Sample Solution:

JavaScript Code:

//#Source https://bit.ly/2neWfJ2 
const isUndefined = val => val === undefined;
console.log(isUndefined(undefined));

Sample Output:

true

Flowchart:

flowchart: Return true if the specified value is undefined, false otherwise

Live Demo:

See the Pen javascript-basic-exercise-185-1 by w3resource (@w3resource) on CodePen.


Improve this sample solution and post your code through Disqus

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JavaScript: Tips of the Day

How to check whether a string contains a substring in JavaScript?

ECMAScript 6 introduced String.prototype.includes:

const string = "foo";
const substring = "oo";

console.log(string.includes(substring));

includes doesn't have Internet Explorer support, though. In ECMAScript 5 or older environments, use String.prototype.indexOf, which returns -1 when a substring cannot be found:

var string = "foo";
var substring = "oo";

console.log(string.indexOf(substring) !== -1);

Ref: https://bit.ly/3fFFgZv