How to check if a value is a number or not a number using JavaScript?
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Question: How to check if a value is a number or not a number using JavaScript? Answer: By using the isNaN() JavaScript function. isNaN = Is Not A Number
Examples:
document.write(isNaN("Hello World!")); //Will print true since Hello World! is not a number
document.write(isNaN(123456)); //Will print false, since 123456 is a number.
var phoneNumber = 0724956785234;
if(isNaN(phoneNumber) == true){
            alert("Please enter a valid phone number");
            return false;
 }
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Javascript 
