JavaScript: Convert String to Number

By Xah Lee. Date: . Last updated: .

JavaScript automatically convert number to string. Adding a string to number results string.

var x = 3 + "4";
console.log(x); // 34
console.log(typeof x); // string

Convert String to Number

parseInt(string,radix) → convert string to a integer number. radix defaults to 10.

parseFloat(string,radix) → convert a string (For example, "3.14") to a decimal number. radix defaults to 10.

// string to number
console.log(
    parseInt("324")  // 324
);

Using the radix argument:

// hexadecimal (as string) to number
console.log(
    parseInt("f", 16)  // 15
)
// binary, using explicit radix
console.log(
    parseInt("10101010", 2)  // 170
)

Convert Number to String

(number).toString(radix) → convert a number to string. radix defaults to 10.

// number to string
console.log(
    (30).toString()             // "30"
);

Number to string, with radix:

// 3 to binary
console.log(
    (3).toString(2)             // "11"
);

// 15 to hex
console.log(
    (15).toString(16)           // "f"
);

ES5 §9#sec-9.8.1

String Topic

  1. JavaScript: Default Charset/Encoding
  2. JavaScript: String is 16-Bit Unit Sequence
  3. JavaScript: Unicode Character Escape Sequence
  4. JavaScript: Allowed Characters in Identifier
  5. HTML: Allowed Characters in id Attribute
  6. HTML: Character Sets and Encoding
  7. HTML XML Entities

  1. JavaScript: Template String
  2. JavaScript: Convert String to Number
  3. JavaScript Encode URL, Escape String
  4. JavaScript: Format Number
  5. JavaScript: JSON Object

  1. JavaScript: String Object
  2. JavaScript: String.prototype
  3. JavaScript: String Constructor

Character Topic

  1. JavaScript: String is 16-Bit Unit Sequence
  2. JavaScript: Convert Character To/From Codepoint
  3. JavaScript: String.fromCodePoint
  4. JavaScript: String.fromCharCode
  5. JavaScript: String.prototype.charAt
  6. JavaScript: String.prototype.charCodeAt
  7. JavaScript: String.prototype.codePointAt
  8. JavaScript: Convert Decimal/Hexadecimal
Like what you read? Buy JavaScript in Depth
or, buy a new keyboard, see Keyboard Reviews.