JavaScript-CheatSheet-en

Modern JavaScript Syntax and Practices CheatSheet

Variable & Expression

Basic Data Type

Regex

  • Symbols

Term

Description

.

(period) Matches any single character, except for line breaks.

*

Matches the preceding expression 0 or more times.

+

Matches the preceding expression 1 or more times.

?

Preceding expression is optional (Matches 0 or 1 times).

^

Matches the beginning of the string.

$

Matches the end of the string.

  • Character groups

Term

Description

\d

Matches any single digit character.

\w

Matches any word character (alphanumeric & underscore).

[XYZ]

Character Set: Matches any single character from the character within the brackets. You can also do a range such as [A-Z]

[XYZ]+

Matches one or more of any of the characters in the set.

Inside a character set, the ^ is used for negation. In this example, match anything that is NOT an uppercase letter.

  • Flags:

    There are five optional flags. They can be used separately or together and are placed after the closing slash. Example: /[A-Z]/g I’ll only be introducing 2 here.

Term

Description

g

Global search

i

case insensitive search

  • Advanced

Term

Description

(x)

Capturing Parenthesis: Matches x and remembers it so we can use it later.

(?:x)

Non-capturing Parenthesis: Matches x and does not remembers it.

x(?=y)

Lookahead: Matches x only if it is followed by y.

Collection

Array

Transform

The reduce() method is used to apply a function to each element in the array to reduce the array to a single value.

Function