Number Methods
JavaScript offers both basic and static number methods to perform operations on, manipulate, and analyze numeric values.
1. Basic Number Methods
These methods can be called on any number or Number object.
toString()
Converts a number to a string, optionally specifying a radix (base).
let num = 42;
console.log(num.toString()); // "42"
console.log(num.toString(2)); // "101010" (binary)
console.log(num.toString(16)); // "2a" (hexadecimal)
toExponential()
Returns a string representing the number in exponential notation with a specified number of digits after the decimal point.
let num = 123.456;
console.log(num.toExponential()); // "1.23456e+2"
console.log(num.toExponential(2)); // "1.23e+2"
toFixed()
Formats a number with a fixed number of digits after the decimal point.
let num = 3.14159;
console.log(num.toFixed(2)); // "3.14"
console.log(num.toFixed(0)); // "3"
toPrecision()
Formats a number to a specified total number of significant digits.
let num = 123.456;
console.log(num.toPrecision(4)); // "123.5"
console.log(num.toPrecision(2)); // "1.2e+2"
valueOf()
Returns the primitive numeric value of a Number object.
let num = new Number(42);
console.log(num.valueOf()); // 42
console.log(typeof num); // "object"
console.log(typeof num.valueOf()); // "number"
2. Static Number Methods
These methods are called on the Number constructor, not individual numbers.
Number.isFinite()
Checks if a value is a finite number (not Infinity, -Infinity, or NaN).
console.log(Number.isFinite(42)); // true
console.log(Number.isFinite(Infinity)); // false
console.log(Number.isFinite(NaN)); // false
console.log(Number.isFinite("42")); // false
Number.isInteger()
Checks if a value is an integer.
console.log(Number.isInteger(42)); // true
console.log(Number.isInteger(42.0)); // true
console.log(Number.isInteger(42.5)); // false
console.log(Number.isInteger("42")); // false
Number.isNaN()
Checks if a value is NaN. Unlike the global isNaN(), it does not convert non-numbers.
console.log(Number.isNaN(NaN)); // true
console.log(Number.isNaN(42)); // false
console.log(Number.isNaN("NaN")); // false
console.log(Number.isNaN(undefined)); // false
Number.isSafeInteger()
Checks if a value is an integer within the safe range (Number.MIN_SAFE_INTEGER to Number.MAX_SAFE_INTEGER).
console.log(Number.isSafeInteger(42)); // true
console.log(Number.isSafeInteger(9007199254740992)); // false
console.log(Number.isSafeInteger(42.5)); // false
console.log(Number.isSafeInteger("42")); // false
Number.parseInt()
Parses a string and returns an integer, optionally specifying a radix.
console.log(Number.parseInt("42")); // 42
console.log(Number.parseInt("42.5")); // 42
console.log(Number.parseInt("1010", 2)); // 10 (binary)
console.log(Number.parseInt("abc")); // NaN
Number.parseFloat()
Parses a string and returns a floating-point number.
console.log(Number.parseFloat("3.14")); // 3.14
console.log(Number.parseFloat("42")); // 42
console.log(Number.parseFloat("3.14abc")); // 3.14
console.log(Number.parseFloat("abc")); // NaNBasic Methods
These methods can be called directly on a number:
| Method | Description | Example |
|---|---|---|
toString() | Converts a number to a string | (123).toString(); // "123" |
toExponential(n) | Returns a string in exponential notation with n decimals | (1234).toExponential(2); // "1.23e+3" |
toFixed(n) | Formats a number with n decimal places | (3.14159).toFixed(2); // "3.14" |
toPrecision(n) | Formats a number to n significant digits | (3.14159).toPrecision(3); // "3.14" |
valueOf() | Returns the primitive value of a number | (123).valueOf(); // 123 |
Static Methods
These methods are called on the Number object, not on individual numbers:
| Method | Description | Example |
|---|---|---|
Number.isFinite(value) | Checks if a value is a finite number | Number.isFinite(10); // true |
Number.isInteger(value) | Checks if a value is an integer | Number.isInteger(10.5); // false |
Number.isNaN(value) | Checks if a value is NaN | Number.isNaN(NaN); // true |
Number.isSafeInteger(value) | Checks if a value is a safe integer | Number.isSafeInteger(9007199254740991); // true |
Number.parseInt(string) | Converts a string to an integer | Number.parseInt("123abc"); // 123 |
Number.parseFloat(string) | Converts a string to a floating-point number | Number.parseFloat("3.14abc"); // 3.14 |