[Javascript] replaceAt and regex matches between symbol

gistfile1.txt

// https://stackoverflow.com/a/1431113/11842937
const replaceAt = function(str, index, replacement) {
    return str.substring(0, index) + replacement + str.substring(index + replacement.length);
}

https://regexr.com/ - regex matches between symbol
regex = new RegExp(`^\\${symbol}(.*)\\${symbol}$`, 'gm')
g = global
m = multiline