Let's say I have this string:

test (string) (10)

How can I get the position of the third parenthesis (second opening)?

This one:

P.S. In real situations I don't control how many characters are inside the parenthesis, so I can't just count them backwards to get a position. I need the index of the third parenthesis wherever it is.

CodePudding user response：

Use indexOf twice, first to get the position of the first closing parentheses, then to get the next opening one:

let s = 'test (string) (10)'
    
let position = s.indexOf('(', s.indexOf(')'))
    
console.log(position)

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Note that position will be zero-based, add 1 if necessary.

CodePudding user response：

Use a regular expression that matches everything up to the third parenthesis, then get its length.

str = 'test (string) (10)';
match = str.match(/^[^(]*\([^)]*\)[^(]*\(/);
if (match) {
  console.log(match[0].length-1);
}

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CodePudding user response：

If the string contains only opening parenthesis that are matched up with a closing parenthesis, you could use a regex with a negated character class \([^()]*\) matching any char other than ( or ) in between the parenthesis.

Then get the index of the second match if it is present:

const s = "test (string) (10)";
const result = [...s.matchAll(/\([^()]*\)/g)];

if (undefined !== result[1]) {
  console.log(result[1].index);
}

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If there can be any unpaired parenthesis, and you just want to match the 3rd one (assuming that using a lookbehind is supported):

const s = "test (string) (10)";
const result = [...s.matchAll(/[()]/g)];

if (undefined !== result[2]) {
  console.log(result[2].index);
}

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CodePudding user response：

The easiest way is definitely not the most performant way.

If performance isn't an issue, I'd personally use split.

var chunks = "test (string) (10)".split("(")

pos = chunks[0].length   chunks[1].length

You may have to add 1 to the formula above or something like that. I don't have time get it just right ;)