Boundaries

Matches beginning of input. If the multiline flag is set to true, also matches immediately after a line break character. For example, /^A/ does not match the "A" in "an A", but does match the first "A" in "An A".

Matches end of input. If the multiline flag is set to true, also matches immediately before a line break character. For example, /t$/ does not match the "t" in "eater", but does match it in "eat".

Matches a word boundary. This is the position where a word character is not followed or preceded by another word-character, such as between a letter and a space. Note that a matched word boundary is not included in the match. In other words, the length of a matched word boundary is zero.

Examples:
/\bm/ matches the 'm' in "moon" ;
/oo\b/ does not match the 'oo' in "moon", because 'oo' is followed by 'n' which is a word character;
/oon\b/ matches the 'oon' in "moon", because 'oon' is the end of the string, thus not followed by a word character;
/\w\b\w/ will never match anything, because a word character can never be followed by both a non-word and a word character.

To match a backspace character ([\b]), see Character Classes.

Matches a non-word boundary. This is a position where the previous and next character are of the same type: Either both must be words, or both must be non-words. Such as between two letters or between two spaces. The beginning and end of a string are considered non-words. Same as the matched word boundary, the matched non-word boundary is also not included in the match. For example, /\Bon/ matches "on" in "at noon", and /ye\B/ matches "ye" in "possibly yesterday".