JavaScript: Return true if the given value is a number, false otherwise

JavaScript fundamental (ES6 Syntax): Exercise-105 with Solution

Check if Value is a Number

Write a JavaScript program that returns true if the given value is a number, false otherwise.

• Use parseFloat() to try to convert n to a number.
• Use !Number.isNaN() to check if num is a number.
• Use Number.isFinite() to check if num is finite.
• Use Number() and the loose equality operator (==) to check if the coercion holds.

Sample Solution:

JavaScript Code:

//#Source https://bit.ly/2neWfJ2

// Define a function 'validateNumber' to check if a value is a valid number.
const validateNumber = n =>
  !isNaN(parseFloat(n)) && // Check if it's a valid number when parsed as a float.
  isFinite(n) && // Check if it's a finite number.
  Number(n) == n; // Check if converting back to a number gives the same value.

// Test the 'validateNumber' function with different inputs.
console.log(validateNumber('200')); // Output: true (valid number)
console.log(validateNumber('10')); // Output: true (valid number)
console.log(validateNumber('abc')); // Output: false (not a valid number)

Output:

true
true
false

Visual Presentation:

Flowchart:

Live Demo:

See the Pen javascript-basic-exercise-105-1 by w3resource (@w3resource) on CodePen.

For more Practice: Solve these Related Problems:

• Write a JavaScript program that returns true if a given value is a number and false otherwise, using typeof and isNaN checks.
• Write a JavaScript function that validates whether an input is a finite number, excluding NaN and Infinity.
• Write a JavaScript program that determines if a value is numeric by testing its conversion to a number and verifying its type.

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