# Strings

In JavaScript, the textual data is stored as strings. There is no separate type for a single character.

The internal format for strings is always [UTF-16](https://en.wikipedia.org/wiki/UTF-16), it is not tied to the page encoding.

## Quotes

Let's recall the kinds of quotes.

Strings can be enclosed within either single quotes, double quotes or backticks:

```js
let single = 'single-quoted';
let double = "double-quoted";

let backticks = `backticks`;
```

Single and double quotes are essentially the same. Backticks, however, allow us to embed any expression into the string, by wrapping it in `${…}`:

```js run
function sum(a, b) {
  return a + b;
}

alert(`1 + 2 = ${sum(1, 2)}.`); // 1 + 2 = 3.
```

Another advantage of using backticks is that they allow a string to span multiple lines:

```js run
let guestList = `Guests:
 * John
 * Pete
 * Mary
`;

alert(guestList); // a list of guests, multiple lines
```

Looks natural, right? But single or double quotes do not work this way.

If we use them and try to use multiple lines, there'll be an error:

```js run
let guestList = "Guests: // Error: Unexpected token ILLEGAL
  * John";
```

Single and double quotes come from ancient times of language creation, when the need for multiline strings was not taken into account. Backticks appeared much later and thus are more versatile.

Backticks also allow us to specify a "template function" before the first backtick. The syntax is: <code>func&#96;string&#96;</code>. The function `func` is called automatically, receives the string and embedded expressions and can process them. This feature is called "tagged templates", it's rarely seen, but you can read about it in the MDN: [Template literals](mdn:/JavaScript/Reference/Template_literals#Tagged_templates).

## Special characters

It is still possible to create multiline strings with single and double quotes by using a so-called "newline character", written as `\n`, which denotes a line break:

```js run
let guestList = "Guests:\n * John\n * Pete\n * Mary";

alert(guestList); // a multiline list of guests, same as above
```

As a simpler example, these two lines are equal, just written differently:

```js run
let str1 = "Hello\nWorld"; // two lines using a "newline symbol"

// two lines using a normal newline and backticks
let str2 = `Hello
World`;

alert(str1 == str2); // true
```

There are other, less common special characters:

| Character | Description |
|-----------|-------------|
|`\n`|New line|
|`\r`|In Windows text files a combination of two characters `\r\n` represents a new break, while on non-Windows OS it's just `\n`. That's for historical reasons, most Windows software also understands `\n`. |
|`\'`,&nbsp;`\"`,&nbsp;<code>\\`</code>|Quotes|
|`\\`|Backslash|
|`\t`|Tab|
|`\b`, `\f`, `\v`| Backspace, Form Feed, Vertical Tab -- mentioned for completeness, coming from old times, not used nowadays (you can forget them right now). |

As you can see, all special characters start with a backslash character `\`. It is also called an "escape character".

Because it's so special, if we need to show an actual backslash `\` within the string, we need to double it:

```js run
alert( `The backslash: \\` ); // The backslash: \
```

So-called "escaped" quotes `\'`, `\"`, <code>\\`</code> are used to insert a quote into the same-quoted string.

For instance:

```js run
alert( 'I*!*\'*/!*m the Walrus!' ); // *!*I'm*/!* the Walrus!
```

As you can see, we have to prepend the inner quote by the backslash `\'`, because otherwise it would indicate the string end.

Of course, only the quotes that are the same as the enclosing ones need to be escaped. So, as a more elegant solution, we could switch to double quotes or backticks instead:

```js run
alert( "I'm the Walrus!" ); // I'm the Walrus!
```

Besides these special characters, there's also a special notation for Unicode codes `\u…`, it's rarely used and is covered in the optional chapter about [Unicode](info:unicode).

## String length

The `length` property has the string length:

```js run
alert( `My\n`.length ); // 3
```

Note that `\n` is a single "special" character, so the length is indeed `3`.

```warn header="`length` is a property"
People with a background in some other languages sometimes mistype by calling `str.length()` instead of just `str.length`. That doesn't work.

Please note that `str.length` is a numeric property, not a function. There is no need to add parenthesis after it. Not `.length()`, but `.length`.
```

## Accessing characters

To get a character at position `pos`, use square brackets `[pos]` or call the method [str.at(pos)](mdn:js/String/at). The first character starts from the zero position:

```js run
let str = `Hello`;

// the first character
alert( str[0] ); // H
alert( str.at(0) ); // H

// the last character
alert( str[str.length - 1] ); // o
alert( str.at(-1) );
```

As you can see, the `.at(pos)` method has a benefit of allowing negative position. If `pos` is negative, then it's counted from the end of the string.

So `.at(-1)` means the last character, and `.at(-2)` is the one before it, etc.

The square brackets always return `undefined` for negative indexes, for instance:

```js run
let str = `Hello`;

alert( str[-2] ); // undefined
alert( str.at(-2) ); // l
```

We can also iterate over characters using `for..of`:

```js run
for (let char of "Hello") {
  alert(char); // H,e,l,l,o (char becomes "H", then "e", then "l" etc)
}
```

## Strings are immutable

Strings can't be changed in JavaScript. It is impossible to change a character.

Let's try it to show that it doesn't work:

```js run
let str = 'Hi';

str[0] = 'h'; // error
alert( str[0] ); // doesn't work
```

The usual workaround is to create a whole new string and assign it to `str` instead of the old one.

For instance:

```js run
let str = 'Hi';

str = 'h' + str[1]; // replace the string

alert( str ); // hi
```

In the following sections we'll see more examples of this.

## Changing the case

Methods [toLowerCase()](mdn:js/String/toLowerCase) and [toUpperCase()](mdn:js/String/toUpperCase) change the case:

```js run
alert( 'Interface'.toUpperCase() ); // INTERFACE
alert( 'Interface'.toLowerCase() ); // interface
```

Or, if we want a single character lowercased:

```js run
alert( 'Interface'[0].toLowerCase() ); // 'i'
```

## Searching for a substring

There are multiple ways to look for a substring within a string.

### str.indexOf

The first method is [str.indexOf(substr, pos)](mdn:js/String/indexOf).

It looks for the `substr` in `str`, starting from the given position `pos`, and returns the position where the match was found or `-1` if nothing can be found.

For instance:

```js run
let str = 'Widget with id';

alert( str.indexOf('Widget') ); // 0, because 'Widget' is found at the beginning
alert( str.indexOf('widget') ); // -1, not found, the search is case-sensitive

alert( str.indexOf("id") ); // 1, "id" is found at the position 1 (..idget with id)
```

The optional second parameter allows us to start searching from a given position.

For instance, the first occurrence of `"id"` is at position `1`. To look for the next occurrence, let's start the search from position `2`:

```js run
let str = 'Widget with id';

alert( str.indexOf('id', 2) ) // 12
```

If we're interested in all occurrences, we can run `indexOf` in a loop. Every new call is made with the position after the previous match:

```js run
let str = 'As sly as a fox, as strong as an ox';

let target = 'as'; // let's look for it

let pos = 0;
while (true) {
  let foundPos = str.indexOf(target, pos);
  if (foundPos == -1) break;

  alert( `Found at ${foundPos}` );
  pos = foundPos + 1; // continue the search from the next position
}
```

The same algorithm can be layed out shorter:

```js run
let str = "As sly as a fox, as strong as an ox";
let target = "as";

*!*
let pos = -1;
while ((pos = str.indexOf(target, pos + 1)) != -1) {
  alert( pos );
}
*/!*
```

```smart header="`str.lastIndexOf(substr, position)`"
There is also a similar method [str.lastIndexOf(substr, position)](mdn:js/String/lastIndexOf) that searches from the end of a string to its beginning.

It would list the occurrences in the reverse order.
```

There is a slight inconvenience with `indexOf` in the `if` test. We can't put it in the `if` like this:

```js run
let str = "Widget with id";

if (str.indexOf("Widget")) {
    alert("We found it"); // doesn't work!
}
```

The `alert` in the example above doesn't show because `str.indexOf("Widget")` returns `0` (meaning that it found the match at the starting position). Right, but `if` considers `0` to be `false`.

So, we should actually check for `-1`, like this:

```js run
let str = "Widget with id";

*!*
if (str.indexOf("Widget") != -1) {
*/!*
    alert("We found it"); // works now!
}
```

### includes, startsWith, endsWith

The more modern method [str.includes(substr, pos)](mdn:js/String/includes) returns `true/false` depending on whether `str` contains `substr` within.

It's the right choice if we need to test for the match, but don't need its position:

```js run
alert( "Widget with id".includes("Widget") ); // true

alert( "Hello".includes("Bye") ); // false
```

The optional second argument of `str.includes` is the position to start searching from:

```js run
alert( "Widget".includes("id") ); // true
alert( "Widget".includes("id", 3) ); // false, from position 3 there is no "id"
```

The methods [str.startsWith](mdn:js/String/startsWith) and [str.endsWith](mdn:js/String/endsWith) do exactly what they say:

```js run
alert( "*!*Wid*/!*get".startsWith("Wid") ); // true, "Widget" starts with "Wid"
alert( "Wid*!*get*/!*".endsWith("get") ); // true, "Widget" ends with "get"
```

## Getting a substring

There are 3 methods in JavaScript to get a substring: `substring`, `substr` and `slice`.

`str.slice(start [, end])`
: Returns the part of the string from `start` to (but not including) `end`.

    For instance:

    ```js run
    let str = "stringify";
    alert( str.slice(0, 5) ); // 'strin', the substring from 0 to 5 (not including 5)
    alert( str.slice(0, 1) ); // 's', from 0 to 1, but not including 1, so only character at 0
    ```

    If there is no second argument, then `slice` goes till the end of the string:

    ```js run
    let str = "st*!*ringify*/!*";
    alert( str.slice(2) ); // 'ringify', from the 2nd position till the end
    ```

    Negative values for `start/end` are also possible. They mean the position is counted from the string end:

    ```js run
    let str = "strin*!*gif*/!*y";

    // start at the 4th position from the right, end at the 1st from the right
    alert( str.slice(-4, -1) ); // 'gif'
    ```

`str.substring(start [, end])`
: Returns the part of the string *between* `start` and `end` (not including `end`).

    This is almost the same as `slice`, but it allows `start` to be greater than `end` (in this case it simply swaps `start` and `end` values).

    For instance:

    ```js run
    let str = "st*!*ring*/!*ify";

    // these are same for substring
    alert( str.substring(2, 6) ); // "ring"
    alert( str.substring(6, 2) ); // "ring"

    // ...but not for slice:
    alert( str.slice(2, 6) ); // "ring" (the same)
    alert( str.slice(6, 2) ); // "" (an empty string)

    ```

    Negative arguments are (unlike slice) not supported, they are treated as `0`.

`str.substr(start [, length])`
: Returns the part of the string from `start`, with the given `length`.

    In contrast with the previous methods, this one allows us to specify the `length` instead of the ending position:

    ```js run
    let str = "st*!*ring*/!*ify";
    alert( str.substr(2, 4) ); // 'ring', from the 2nd position get 4 characters
    ```

    The first argument may be negative, to count from the end:

    ```js run
    let str = "strin*!*gi*/!*fy";
    alert( str.substr(-4, 2) ); // 'gi', from the 4th position get 2 characters
    ```

    This method resides in the [Annex B](https://tc39.es/ecma262/#sec-string.prototype.substr) of the language specification. It means that only browser-hosted Javascript engines should support it, and it's not recommended to use it. In practice, it's supported everywhere.

Let's recap these methods to avoid any confusion:

| method | selects... | negatives |
|--------|-----------|-----------|
| `slice(start, end)` | from `start` to `end` (not including `end`) | allows negatives |
| `substring(start, end)` | between `start` and `end` (not including `end`)| negative values mean `0` |
| `substr(start, length)` | from `start` get `length` characters | allows negative `start` |

```smart header="Which one to choose?"
All of them can do the job. Formally, `substr` has a minor drawback: it is described not in the core JavaScript specification, but in Annex B, which covers browser-only features that exist mainly for historical reasons. So, non-browser environments may fail to support it. But in practice it works everywhere.

Of the other two variants, `slice` is a little bit more flexible, it allows negative arguments and shorter to write.

So, for practical use it's enough to remember only `slice`.
```

## Comparing strings

As we know from the chapter <info:comparison>, strings are compared character-by-character in alphabetical order.

Although, there are some oddities.

1. A lowercase letter is always greater than the uppercase:

    ```js run
    alert( 'a' > 'Z' ); // true
    ```

2. Letters with diacritical marks are "out of order":

    ```js run
    alert( 'Österreich' > 'Zealand' ); // true
    ```

    This may lead to strange results if we sort these country names. Usually people would expect `Zealand` to come after `Österreich` in the list.

To understand what happens, we should be aware that strings in Javascript are encoded using [UTF-16](https://en.wikipedia.org/wiki/UTF-16). That is: each character has a corresponding numeric code.

There are special methods that allow to get the character for the code and back:

`str.codePointAt(pos)`
: Returns a decimal number representing the code for the character at position `pos`:

    ```js run
    // different case letters have different codes
    alert( "Z".codePointAt(0) ); // 90
    alert( "z".codePointAt(0) ); // 122
    alert( "z".codePointAt(0).toString(16) ); // 7a (if we need a hexadecimal value)
    ```

`String.fromCodePoint(code)`
: Creates a character by its numeric `code`

    ```js run
    alert( String.fromCodePoint(90) ); // Z
    alert( String.fromCodePoint(0x5a) ); // Z (we can also use a hex value as an argument)
    ```

Now let's see the characters with codes `65..220` (the latin alphabet and a little bit extra) by making a string of them:

```js run
let str = '';

for (let i = 65; i <= 220; i++) {
  str += String.fromCodePoint(i);
}
alert( str );
// Output:
// ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~
// ¡¢£¤¥¦§¨©ª«¬­®¯°±²³´µ¶·¸¹º»¼½¾¿ÀÁÂÃÄÅÆÇÈÉÊËÌÍÎÏÐÑÒÓÔÕÖ×ØÙÚÛÜ
```

See? Capital characters go first, then a few special ones, then lowercase characters, and `Ö` near the end of the output.

Now it becomes obvious why `a > Z`.

The characters are compared by their numeric code. The greater code means that the character is greater. The code for `a` (97) is greater than the code for `Z` (90).

- All lowercase letters go after uppercase letters because their codes are greater.
- Some letters like `Ö` stand apart from the main alphabet. Here, its code is greater than anything from `a` to `z`.

### Correct comparisons [#correct-comparisons]

The "right" algorithm to do string comparisons is more complex than it may seem, because alphabets are different for different languages.

So, the browser needs to know the language to compare.

Luckily, modern browsers support the internationalization standard [ECMA-402](https://www.ecma-international.org/publications-and-standards/standards/ecma-402/).

It provides a special method to compare strings in different languages, following their rules.

The call [str.localeCompare(str2)](mdn:js/String/localeCompare) returns an integer indicating whether `str` is less, equal or greater than `str2` according to the language rules:

- Returns a negative number if `str` is less than `str2`.
- Returns a positive number if `str` is greater than `str2`.
- Returns `0` if they are equivalent.

For instance:

```js run
alert( 'Österreich'.localeCompare('Zealand') ); // -1
```

This method actually has two additional arguments specified in [the documentation](mdn:js/String/localeCompare), which allows it to specify the language (by default taken from the environment, letter order depends on the language) and setup additional rules like case sensitivity or should `"a"` and `"á"` be treated as the same etc.

## Summary

- There are 3 types of quotes. Backticks allow a string to span multiple lines and embed expressions `${…}`.
- We can use special characters, such as a line break `\n`.
- To get a character, use: `[]`.
- To get a substring, use: `slice` or `substring`.
- To lowercase/uppercase a string, use: `toLowerCase/toUpperCase`.
- To look for a substring, use: `indexOf`, or `includes/startsWith/endsWith` for simple checks.
- To compare strings according to the language, use: `localeCompare`, otherwise they are compared by character codes.

There are several other helpful methods in strings:

- `str.trim()` -- removes ("trims") spaces from the beginning and end of the string.
- `str.repeat(n)` -- repeats the string `n` times.
- ...and more to be found in the [manual](mdn:js/String).

Strings also have methods for doing search/replace with regular expressions. But that's big topic, so it's explained in a separate tutorial section <info:regular-expressions>.

Also, as of now it's important to know that strings are based on Unicode encoding, and hence there're issues with comparisons. There's more about Unicode in the chapter <info:unicode>.