How to Convert Values to Numbers in Javascript

While dealing with mathematical calculations we need to make sure that the variable in question is actually a number. For this we can convert the variable into a number.

A value can be converted to a number using the global Number() method. This method accepts a value of any type as parameter and converts it to a number following a set of rules. If it cannot be converted to a number, it returns NaN which basically means "not a number".

undefined to Number

If undefined is passed as parameter, Number() returns NaN.

var a = undefined;

// NaN
console.log(Number(a));

null to Number

If null is passed to Number(), it returns 0.

var a = null;

// 0
console.log(Number(a));

boolean to Number

A boolean true is returned as 1, false is returned as 0.

var a = true;

var b = false;

// 1
console.log(Number(a));

// 0
console.log(Number(b));

string to Number

An empty string passed to Number() is returned as 0.

var a = '';

// 0
console.log(Number(a));

A non-empty string is parsed to get a number from it. Trailing and leading whitespaces (including tabs and newlines) are removed. After removal if the contents represent a number, it is returned. If it does not represent a number then NaN is returned.

// 23.5
console.log(Number("\t  23.5 \t\t"));

// NaN
console.log(Number("abc"));

// NaN
console.log(Number("23abc"));

number to Number

If a number is passed to Number(), the same value is returned.

// 100
console.log(Number(100));

Checking for NaN

When Number() returns NaN, it needs to be handled. The method Number.isNaN() checks whether the value passed represents NaN or not.

var a = 'abc';

// NaN
var a_numeric = Number(a);

if(Number.isNaN(a_numeric))
    console.log('Not a Number');
else
    console.log('Valid Number');