Strange spaces in javascript regex

Question

I saw this weird regular expression in javascript.

string = "abababababababa";
string=string.replace(/ ?a ?/g,"X");
alert(string);  

I ran it, and the result that I got was replaced with X. What causes bewilderment are spaces in the regular expression. I delete the first empty space, the script will not work. I delete the second empty space, I get one "a" replaced by two "X". I wonder how it works.

Answer 1

Space actually means a white space match (U + 0020).

? quantifier, , "0 1 " , .

, / ?a ?/ :

• "a"
• "a "
• " a"
• " a "

:

• (/?a ?/g) SyntaxError, - .

• (/ ?a?/g) , ? a, :

  • ""
  • "a"
  • " "
  • " a"

Answer 2

? .

, X .

> "a"
> " a"
> " a "
> "a "

.

Answer 3

' ' . ? 1 0 .

:

 ?          ' ' optional space character
a           match 'a'
 ?          ' ' optional space character

:

• 'a'
• 'a '
• ' a'
• ' a '

a b a b a b a b a b a b a b a g (global ). ( )

• , , .

• If you leave a space character but delete the first one ?, it will be disabled because it looks like a space character, however, a space does not exist at the input.

• If you delete the second space character, it still manages to combine awith the option.