Javascript number function examples

Learn javascript number function to check input is a number, how to check range, eval function example.

In JavaScript there is only one type for all numbers, all numbers are treated as floating-point numbers. though the dot is not displayed if there is no digit after the decimal point.

Converting to Number

JavaScript has in-built Number Function
Let's take a look at some example how to convert different object values to numbers using Number() Function in JavaScript

<script>
    var a1 = new Date();
    var a2 = true;
    var a3 = false;
    var a4 = 99.99;
    var a5 = "999";
    var a6 = "999 888";
                
    document.write(Number(a1));
      
    document.write(Number(a2));
         
    document.writeln(Number(a3));
       
    document.writeln(Number(a4));
        
    document.writeln(Number(a5));
         
    document.writeln(Number(a6));
</script>
    

How to use eval function in JavaScript

Now think of a situation where you receive user input as number and do some calculation based on that. Suppose you receive a number as string, but you need to perform some calculation, in such scenario you have to use eval() function.

eval() is used for evaluating the expression

<script>
    var n1 = 10;
    var n2 = 5;
    var stringFormat = n1 + " + " + n2;
    document.writeln(stringFormat); // 10 + 5
    // using eval method
    document.writeln(eval(stringFormat)); // 15
</script>

Number to String in JavaScript

There is built-in toString() method in javscript to convert a integer value to a string.

            var x = 721;  
x.toString();            // returns 721 from variable x
(123).toString();        // returns 721 from literal 123 
(700 + 21).toString();   // returns 721 from expression 700 + 21
                

Check input is number in JavaScript

You can check input is number in JavaScript using isNaN function this is a built-in function, simply check if input is a number.

var inputV1="Your Age?";

if(isNaN(inputV1))
    console.log("Please enter number");
else 
    console.log("You are "+ inputV1);

Check number range in javascript

If you want to check if any number is within specified range using JavaScript, there is no built-in function to check range, but you can create a function like example below, here we have three parameters to the function, input value, minimum value and maximum limit.

function isInRange(input, min, max) {
return ((input-min)*(input-max) <= 0);
}
    
console.log(isInRange(4, 1, 10));     // true
console.log(isInRange(-2, 1, 10));    // false
console.log(isInRange(11, 1, 10));    // false

The above JavaScript function to check range- is a custom function, you can give any name; also can change the internal logic if you find more efficient way to do it.