Menu
I have read recently about JavaScript regular expressions, but I am confused.
The author says that it is necessary to include the caret (^) and dollar symbol ($) at the beginning and end of the all regular expressions declarations.
Why are they needed?
543
You can use the caret symbol (^) at the start of a regular expression to indicate that a match must occur at the beginning of the searched text.
If a dollar sign ( $ ) is at the end of the entire regular expression, it matches the end of a line. If an entire regular expression is enclosed by a caret and dollar sign ( ^like this$ ), it matches an entire line.
One can denote the position of a pattern within a string. The caret (^) denotes the beginning of the string. The pattern "^abc" will match a string starting with abc. The dollar sign ($) denotes the end of the string.
. means match any character in regular expressions. * means zero or more occurrences of the SINGLE regex preceding it.
Javascript RegExp() allows you to specify a multi-line mode (m) which changes the behavior of ^ and $.
^ represents the start of the current line in multi-line mode, otherwise the start of the string
$ represents the end of the current line in multi-line mode, otherwise the end of the string
For example: this allows you to match something like semicolons at the end of a line where the next line starts with "var" /;$\n\s*var/m
Fast regexen also need an "anchor" point, somewhere to start it's search somewhere in the string. These characters tell the Regex engine where to start looking and generally reduce the number of backtracks, making your Regex much, much faster in many cases.
NOTE: This knowledge came from Nicolas Zakas's High Performance Javascript
Conclusion: You should use them!
172
^ represents the start of the input string.
$ represents the end.
You don't actually have to use them at the start and end. You can use em anywhere =) Regex is fun (and confusing). They don't represent a character. They represent the start and end.
This is a very good website
31
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
