JS: String Overview

By Xah Lee. Date: . Last updated: .

String is one of the type of JavaScript values.

[see JS: Value Types]

// example of string
console.log ( "hello" );

String is a Primitive Value

JS: Primitive Value

String is Immutable

JavaScript string is immutable. That means, any time you join string or get a substring or replace parts of the string, a new string is created.

All JavaScript string methods return a new string.

In practice, this means, if you need to create a long string, such as repeatedly append to a string one thousand times, you should not use a loop with append to do that. Because, the process of creating a long string is expensive. (The workaround in this case is to use a array. Push string to the array, then use Array.prototype.join to convert it to string.)

String is 16 Bits Unit Sequence

Technically, each character in string is a 16 bits unit, not a character.

This is important when your string contains Unicode character such as emoji 😸.

[see JS: Character, Code Unit, Code Point]

String Escape Sequence

Backslash sequence such as \n is called escape sequence.

console.log ( "a\nb" );
// prints a and b each on its own line
// the \n is a escape sequence. It means newline

[see JS: String Escape Sequence]

Unicode Escape Sequence

JS: Unicode Escape Sequence

Create String

Literal String Expression

Use double quote or single quote for string. There's basically no difference between the two.

const s1 = "Mary's cat";
// double quote

const s2 = 'Mary\'s cat';
// single quote, with escape

Use \n for newline.

// use \n for newline
const ss = "cat\ndog";

console.log(ss); // prints 2 lines

Literal newline in string is not allowed. Use backslash to continue a line.

// illegal syntax. Literal newline is not allowed
const s = "a
b";

// use backslash to continue a line
const s = "c\
d";

console.log(s); // prints cd

Template String

String can also be quoted by using GRAVE ACCENT `, like this:

let x = `something`;

Expression of the form ${expression} in template string is evaluated.

console.log ( `I have ${1 + 1} cats` );
// I have 2 cats

[see JS: Template String]

String Constructor

String value can also be created by using the constructor function String.

But it's not a good practice, because there is no use of it that's not better done with string literal expression.

[see JS: String Constructor]

[see JS: String Object]

+ for Join String

JavaScript's plus operator + is also used to join string, like this:

"a" + "b" + "c"

console.log ( "a" + "b" + "c" ===  "abc"); // true

String Methods

JS: String.prototype

Convert Character To/From Codepoint

JS: Convert Character To/From Codepoint

JS String

  1. String Overview
  2. Template String
  3. Char, Code Unit, Code Point
  4. String Escape Sequence
  5. Unicode Escape Sequence
  6. String to Number
  7. Encode URL, Escape String
  8. Format Number
  9. Source Code Encoding
  10. Allowed Characters in Identifier
  11. String Object
  12. String.prototype
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