How to replace characters from the beginning of a String
I needed to replace the leading tabs to two s in one of my projects. Javascript offers a replace function that seems fit for this task, but unfortunately, it seems there are no trivial solutions.
Using /\t/g matches all the tabs, not just the leading ones:
"\tstr\t".replace(/\t/g, " ")
// " str "
By modifying the expression to only match tabs from the beginning only inserts the replacement text once:
"\t\tstr\t".replace(/^\t+/, " ")
// " str\t"
Using a replacer function
Fortunately, replace also accepts a replacer function instead of a replacement text.
The only problem with the /^\t+/ solution is that it matches all the leading tabs. The replacer function then gets a String containing all of them.
So the only thing needed is to replace all characters in that String to the target text.
A trivial solution is to convert the String to a character Array, map all elements and join them together:
"\t\tstr\t".replace(
/^\t+/,
(tabs) => tabs.
split("").
map(() => " ").
join("")
)
// " str\t"
Note: Instead of tabs.split(""), [...tabs] works as well. This is because a String is an iterable structure and [...tabs] converts it to a full-fledged Array.
Another solution is to use replace again to match and replace all characters:
"\t\tstr\t".replace(
/^\t+/,
(tabs) => tabs.
replace(
/./g,
" "
)
)
// " str\t"