Replaces all regular expression patterns in a string with dynamic data from a map.

replacer.js

function makeReplacer(str) {
    const regex = /\$\w+\.(\w+)/g;
    let strFragments = []; // stores static strings, or a function to get value from map
    let m; // regex match object
    let idx; // index tracking the position of one match in `str`
    while ((m = regex.exec(str)) !== null) {
        // This is necessary to avoid infinite loops with zero-width matches
        if (m.index === regex.lastIndex) {
            regex.lastIndex++;
        }
        strFragments.push(str.substring(idx, m.index))
        strFragments.push(
            (key => {
                return map => map[key]
            })(m[1])
        ) // needs two lambdas, because we are passing m[1] as value to the inner lambda
        idx = m.index + m[0].length
    }
    if (idx < str.length) {
        strFragments.push(str.substring(idx))
    }
    return (varMap) => {
        return strFragments.map(sf => {
            if (typeof sf === 'string') {
                return sf
            }
            return sf(varMap)
        }).join('')
    };
}

const str = `value $data.num1 + $data.num2 = $data.sum, right?`;
let replacer = makeReplacer(str)
let varMap = {
    num1: 1,
    num2: 2,
    sum: 3,
}
console.log(replacer(varMap))
varMap['sum'] = 4
console.log(replacer(varMap))