I'm trying to make a function to get the beginning and end of part of a string similar to a code block, returning the corresponding character index. Example:
abc [ //A0 - start
def [ //B1 - start
ghi [ //C2 - start
jkl
] //D2 - end
] //E1 - end
] //F0 - end
then a getBlock function would receive the string and index of one of the characters ("[" or "]") and return the index of its corresponding partner:
var str = "abc [def [ghi [jkl]]]";
getBlock(str, 4); // returns 20 ("F0" in the example)
getBlock(str, 9); // returns 19 ("E1")
getBlock(str, 14); // returns 18 ("D2")
getBlock(str, 20); // returns 4 ("A0")
getBlock(str, 19); // returns 9 ("B1")
getBlock(str, 18); // returns 14 ("C2")
This is my functional attempt so far:
function getBlock(str) {
console.log({
"start": Array.from(str.matchAll(/\[/g)).map(m => m.index),
"end": Array.from(str.matchAll(/\]/g)).map(m => m.index)
})
}
getBlock("abc [def [ghi [jkl]]]")It returns two arrays containing the index of all start and end characters, but I still haven't been able to figure out a logic to get its partners individually, any idea if that's possible?
Ok I ended up creating a somewhat ugly solution, but it seems to work as expected:
function getBlock(str, i) {
var blocks = Array.from(str.matchAll(/\[|]/g)).map(m => m.index);
return blocks[(blocks.length-blocks.indexOf(i))-1];
}
// must return 20 19 18 4 9 14
var str = "abc [def [ghi [jkl]]]";
console.log(
getBlock(str, 4),
getBlock(str, 9),
getBlock(str, 14),
getBlock(str, 20),
getBlock(str, 19),
getBlock(str, 18)
);
the logic is very simple, instead of returning two arrays it returns only one:
[4, 9, 14, 18, 19, 20]
from there you just need to get the values from the "middle":
14 18
9 19
4 20
and that's it.
Edit: It works for the case where each block has only one block inside it, but if there are two blocks side by side it doesn't. Example where it fails:
var str = "abc [def] [ghi]";
getBlock(str, 10) // returns 8 instead of 14
Edit 2 (Solution):
Okay this should be the proper JavaScript solution, inspired by @HereticMonkey's comment regarding How do I find the position of matching parentheses or braces in a given piece of text?, the only difference is that this version is in JavaScript and has been slightly changed to allow start and end indexes.
function getBlock(str, start) {
var end = start;
var counter = 1;
while (counter > 0) {
var direction = (symbol) => ((str[start] == symbol) ? 1 : -1);
var char = str[end += direction("[")];
if (char == "[" || char == "]") {
counter += direction(char)
};
}
return {
"start": start,
"end": end
};
}
var str = "abc [def [ijk]] [ghi]";
console.log(
getBlock(str, 4), // {start: 4, end: 14}
getBlock(str, 9), // {start: 9, end: 13}
getBlock(str, 16) // {start: 16, end: 20}
);