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JavaScript: strings

A string is a sequence of characters. That is not quite true for Unicode. An Unicode string is a sequence of “code points”. JavaScript support Unicode symbols in string literals. 

String literals

String literals are surrounded by single quotes: ‘…’ or double quotes “…”. You can use quotes inside a string, as long as they don’t match the quotes surrounding the string, otherwise you must use escape symbol “\” in front of quotes matching the surrounding quotes. 

Example:

Join two strings:

The process of joining two strings is also called concatenation. We create a new string using concatenate operator “+”.  Below is an example of concatenating two string variables.

Template literals

Templates are special string literals enclosed in back-quotes `…` There is a useful method for string manipulation called: “string interpolation”. For this string template can use placeholders like: ${var}. A placeholder will be replace automatically by values.

Example: 

Notes:

  • String templates can include single quotes or double quotes
  • Back-quotes must be escaped with “\”  inside a template
  • String interpolation can accept numeric variables
  • String interpolation can accept expressions

Example:

Output:

5 + 10 = 15
2 * (5 + 10) = 20

Split a string:

A string is an object so it has methods. String methods can be call using the dot notation. For example if str=”Hello World” is a sting then you can use method: split like this: str.split(” “) and this will create an array of 2 words: [“Hello”,”World”]. The string was split in two parts and space (the separator) is discarded.

Extract a character:

There are 2 safe methods for extracting string characters:

  • charAt(position)
  • charCodeAt(position)

Example:

Note: Do not use a string like an array with index: str[0]. This is not safe, except if your string is using ASCII characters or printable Unicode symbols and no modifiers. If this is not true accessing a string character by index is a bad practice.

String methods

The string object has numerous predefined methods that are not in my scope to present. If you need a method you should consult the MDN reference documentation. To search this documentation type in google search box: MDN <function_name> for example: “mdn charAt()”, most of the time first hit will lead you to details about correct function.

MethodDescription
charAt()Returns the character at the specified index (position)
charCodeAt()Returns the Unicode of the character at the specified index
concat()Joins two or more strings, and returns a new joined strings
endsWith()Checks whether a string ends with specified string/characters
fromCharCode()Converts Unicode values to characters
includes()Checks whether a string contains the specified string/characters
indexOf()Returns the position of the first found occurrence of a specified value in a string
lastIndexOf()Returns the position of the last found occurrence of a specified value in a string
localeCompare()Compares two strings in the current locale
match()Searches a string for a match against a regular expression, and returns the matches
repeat()Returns a new string with a specified number of copies of an existing string
replace()Searches a string for a specified value, or a regular expression, and returns a new string where the specified values are replaced
search()Searches a string for a specified value, or regular expression, and returns the position of the match
slice()Extracts a part of a string and returns a new string
split()Splits a string into an array of substrings
startsWith()Checks whether a string begins with specified characters
substr()Extracts the characters from a string, beginning at a specified start position, and through the specified number of character
substring()Extracts the characters from a string, between two specified indices
toLocaleLowerCase()Converts a string to lowercase letters, according to the host’s locale
toLocaleUpperCase()Converts a string to uppercase letters, according to the host’s locale
toLowerCase()Converts a string to lowercase letters
toString()Returns the value of a String object
toUpperCase()Converts a string to uppercase letters
trim()Removes white-space from both ends of a string

reference manual: MDN: String Methods

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