JavaScript Strings

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JavaScript Strings

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JavaScript strings are used for storing and manipulating text.

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JavaScript Strings

A JavaScript string simply stores a series of characters like "John Doe".

A string can be any text inside quotes. You can use single or double quotes:

문자열을 나타낼 때 , 작은 따옴표 , 큰 따옴표 둘다 사용가능.

Example

var carname = "Volvo XC60";
var carname = 'Volvo XC60';

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You can use quotes inside a string, as long as they don't match the quotes surrounding the string:

" sssss 'A' "

' sssss "A" ' 안에 것과 밖에 것이 중복되지 않으면 사용가능. 

Example

var answer = "It's alright";
var answer = "He is called 'Johnny'";
var answer = 'He is called "Johnny"';

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String Length

The length of a string is found in the built in property length:

Example

var txt = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
var sln = txt.length;

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Special Characters

Because strings must be written within quotes, JavaScript will misunderstand this string:

var y = "We are the so-called "Vikings" from the north."

The string will be chopped to "We are the so-called ".

The solution to avoid this problem, is to use the \ escape character.

The backslash escape character turns special characters into string characters:

Example

var x = 'It\'s alright';
var y = "We are the so-called \"Vikings\" from the north."

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The escape character (\) can also be used to insert other special characters in a string.

This is the list of special characters that can be added to a text string with the backslash sign:

Code	Outputs
\'	single quote
\"	double quote
\\	backslash
\n	new line
\r	carriage return
\t	tab
\b	backspace
\f	form feed

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Breaking Long Code Lines

For best readability, programmers often like to avoid code lines longer than 80 characters.

If a JavaScript statement does not fit on one line, the best place to break it is after an operator:

Example

document.getElementById("demo").innerHTML =
"Hello Dolly.";

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You can also break up a code line within a text string with a single backslash:

Example

document.getElementById("demo").innerHTML = "Hello \
Dolly!";

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	The \ method is not a ECMAScript (JavaScript) standard. Some browsers do not allow spaces behind the \ character.

The safest (but a little slower) way to break a long string is to use string addition:

Example

document.getElementById("demo").innerHTML = "Hello" + 
"Dolly!";

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You cannot break up a code line with a backslash:

Example

document.getElementById("demo").innerHTML = \ 
"Hello Dolly!";

Try it Yourself »

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Strings Can be Objects

Normally, JavaScript strings are primitive values, created from literals: var firstName = "John"

But strings can also be defined as objects with the keyword new: var firstName = new String("John")

Example

var x = "John";
var y = new String("John");

// typeof x will return string
// typeof y will return object

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	Don't create strings as objects. It slows down execution speed. The new keyword complicates the code. This can produce some unexpected results:

When using the == equality operator, equal strings looks equal:

Example

var x = "John";             
var y = new String("John");

// (x == y) is true because x and y have equal values

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When using the === equality operator, equal strings are not equal, because the === operator expects equality in both type and value.

Example

var x = "John";             
var y = new String("John");

// (x === y) is false because x and y have different types (string and object)

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Or even worse. Objects cannot be compared:

Example

var x = new String("John");             
var y = new String("John");

// (x == y) is false because x and y are different objects
// (x == x) is true because both are the same object

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	JavaScript objects cannot be compared.

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String Properties and Methods

Primitive values, like "John Doe", cannot have properties or methods (because they are not objects).

But with JavaScript, methods and properties are also available to primitive values, because JavaScript treats primitive values as objects when executing methods and properties.

String methods are covered in next chapter.

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String Properties

Property	Description
constructor	Returns the function that created the String object's prototype 객체를 만드는 함수를 반환하거나 설정하는 메소드
length	Returns the length of a string 문자열길이 반환
prototype	Allows you to add properties and methods to an object 객체에 속성과 메소드 추가

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String Methods

Method	Description
charAt()	Returns the character at the specified index (position) 문자열에서 특정 위치의 문자를 반환
charCodeAt()	Returns the Unicode of the character at the specified index 문자열에서 특정 위치의 문자의 유니코드 값을 반환
concat()	Joins two or more strings, and returns a copy of the joined strings 2개의 문자열을 하나으 문자열로 만든다.
fromCharCode()	Converts Unicode values to characters 유니코드에서 글자를 반환
indexOf()	Returns the position of the first found occurrence of a specified value in a string 문자열에서 특정 문자가 있는 위치를 반환. indexOf(찾을 문자 , 찾기 시작할 위치)
lastIndexOf()	Returns the position of the last found occurrence of a specified value in a string indexOf()와 같은 기능이나 문자열의 오른쪽에서 왼쪽으로 찾는다.
localeCompare()	Compares two strings in the current locale 문자열과 문자열 비교
match()	Searches a string for a match against a regular expression, and returns the matches 문자열에서 특정 정규 표현식과 매칭되는 문자열을 배열로 반환
replace()	Searches a string for a value and returns a new string with the value replaced 기존문자나 정규표현식을 특정문자열로 변경
search()	Searches a string for a value and returns the position of the match 문자열에서 문자나 정규표현식을 검색한 것의 index를 반환
slice()	Extracts a part of a string and returns a new string 문자열 일부 추출
split()	Splits a string into an array of substrings 문자열을 분리
substr()	Extracts a part of a string from a start position through a number of characters 문자열을 length만큼 잘라내기
substring()	Extracts a part of a string between two specified positions 매개변수1과 2사이에있는 문자열을 반환
toLocaleLowerCase()	Converts a string to lowercase letters, according to the host's locale 모든 영문자를 소문자로 변경
toLocaleUpperCase()	Converts a string to uppercase letters, according to the host's locale 모든 영문자를 대문자로 변경
toLowerCase()	Converts a string to lowercase letters 지정된 문자열을 모두 소문자로 변경
toString()	Returns the value of a String object 숫자를 문자열로 바꿈
toUpperCase()	Converts a string to uppercase letters 지정된 문자열을 모두 대문자로 변경
trim()	Removes whitespace from both ends of a string 문자열 양쪽의 공백제거
valueOf()	Returns the primitive value of a String object 객체의 원래 값을 반환

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