How to match the exact string and replace all with other string using regular expression?

[skihouston]

Recently I came across one issue where I need to change the double curly braces with triple curly braces ,
The below example could clarify the need further,
let mystring = '{{Hello Tom}} , {{How are you doing today}}'

I need to change the above string and replace "{{" and "}}" with "{{{" and "}}}" respectively.
Currently I am using regex as below,
let output_string = mystring.replace(/{{/g, "{{{").replace(/}}/g, "}}}")

At the first execution its working fine and I got the desired output as '{{{Hello Tom}}} , {{{How are you doing today}}}' , when the next execution happen , it changed to 4 curly braces like below,
Output after second execution,
'{{{{Hello Tom}}}} , {{{{How are you doing today}}}}'

Its keep on increasing the curly braces whenever event is repeated.
I just want to replace 2 curly braces with 3,not any further
How can I Achieve this ???

 

[fonehe5161]

You can do it like this:

const output = input.replace(/\{+(.*?)\}+/g, (match, p1) => {
  return `{{{${p1}}}}`;
});

The regular expression pattern /\{+(.*?)\}+/g matches any number of curly braces, including none, and captures the text inside the braces in group 1.

Demo

const input = '{{Hello Tom}} , {{How are you doing today}}';

const input2 = '{{{Hello Tom}}} , {{{How are you doing today}}}';

const input3 = '{{{{Hello Tom}}}} , {{{{How are you doing today}}}}';

const output = input.replace(/\{+(.*?)\}+/g, (match, p1) => {
  return `{{{${p1}}}}`;
});

const output2 = input2.replace(/\{+(.*?)\}+/g, (match, p1) => {
  return `{{{${p1}}}}`;
});

const output3 = input3.replace(/\{+(.*?)\}+/g, (match, p1) => {
  return `{{{${p1}}}}`;
});

console.log(output)
console.log(output2)
console.log(output3)