JavaScript

JavaScript provides several built-in methods to work with numbers. These methods help you format, convert, and manipulate numbers easily.

Let’s explore the most commonly used number methods in JavaScript.

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✅ 1. toString()

Converts a number into a string.

let num = 123;
let str = num.toString();
console.log(str);        // Output: "123"
console.log(typeof str); // Output: "string"

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✅ 2. toFixed(n)

Returns a string with the number rounded to n decimal places.

let price = 99.456;
console.log(price.toFixed(2)); // Output: "99.46"

Great for showing prices and controlling decimal output.

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✅ 3. toExponential(n)

Returns the number in exponential notation with n decimals.

let num = 12345;
console.log(num.toExponential(2)); // Output: "1.23e+4"

Used in scientific calculations.

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✅ 4. toPrecision(n)

Formats a number to a specified total number of digits (not just decimals).

let num = 9.8765;
console.log(num.toPrecision(3)); // Output: "9.88"

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✅ 5. valueOf()

Returns the primitive value of a number. This is rarely used because JavaScript automatically calls it.

let x = 50;
console.log(x.valueOf()); // Output: 50

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✅ 6. Number.isInteger()

Checks if a value is an integer.

console.log(Number.isInteger(10));   // true
console.log(Number.isInteger(10.5)); // false

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✅ 7. Number.isNaN()

Checks if a value is NaN (Not a Number).

console.log(Number.isNaN("hello"));         // false
console.log(Number.isNaN(NaN));             // true
console.log(Number.isNaN(100 / "apple"));   // true

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✅ 8. Number.parseInt()

Converts a string to an integer.

let str = "42.9";
console.log(Number.parseInt(str)); // Output: 42

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✅ 9. Number.parseFloat()

Converts a string to a floating-point number.

let str = "42.9";
console.log(Number.parseFloat(str)); // Output: 42.9

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✅ 10. Number.isFinite()

Checks if a value is a finite number (not Infinity, -Infinity, or NaN).

console.log(Number.isFinite(100));       // true
console.log(Number.isFinite(Infinity));  // false

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🧠 Summary Table

Method	Description	Example
toString()	Converts number to string	(123).toString() → "123"
toFixed(n)	Rounds to n decimal places	(5.678).toFixed(2) → "5.68"
toExponential(n)	Exponential notation with n decimals	(1234).toExponential(1) → "1.2e+3"
toPrecision(n)	Formats to n digits	(3.14159).toPrecision(3) → "3.14"
valueOf()	Gets the primitive number value	(100).valueOf() → 100
Number.isInteger()	Checks if value is an integer	true / false
Number.isNaN()	Checks if value is NaN	true / false
parseInt()	Converts string to integer	"55px" → 55
parseFloat()	Converts string to float	"5.5px" → 5.5
isFinite()	Checks if value is finite	true / false

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