What does this regular expression: /[\[]/?

Question

I am struggling to understand what this means: /[\[]/ Why are there two replace statements?

name = name.replace(/[\[]/, "\\\[").replace(/[\]]/, "\\\]");

Answer 1

/[\[]/ is a regular expression literal.

In the first replacement, you're replacing a [ by \[ and the symetric in the second one.

It looks weird because of many (mostly useless) escapements : [ is escaped in the regex and \ and [ are escaped in the string literal.

The first regex can be analyzed like this :

• / : regex opening
• [ : character set opening
• \[ : the [ character (with an escaping that is useless as it's in a set)
• ] : character set closing
• / : regex closing

Those regexes look too verbose to me : you don't need a character set if you have just one character in that set. And you don't need to escape the [ in the string literal.

You could have done

 name = name.replace(/\[/, "\\[").replace(/\]/, "\\]");

For example

 'a [ b c ] d [ e ]'.replace(/\[/, "\\[").replace(/\]/, "\\]")

gives

 "a \[ b c \] d [ e ]"

Note that as there is no g modifier, you're only doing one replacement in each call to replace, which probably isn't the goal, so you might want

 name = name.replace(/\[/g, "\\[").replace(/\]/g, "\\]");