Replace variables in a string (JS one-liner)

str_replace.js

// one-liner version
('hello {name}') // input string
  .split('{') // start of variable
  .map(s => s.split('}')) // end of variable
  .flat()
  .map((s, i) => i & 1 ? ({ name: 'world' })[s] ?? `{${s}}` : s) // variable lookup with fallback
  .join(''); //> "hello world"

// with variables
const inputString = 'hello {name}';
const varStart = '{';
const varEnd = '}';
const variables = {
  name: 'world'
};

const outputString = inputString
  .split(varStart)
  .map(s => s.split(varEnd))
  .flat()
  .map((s, i) => i & 1 ? variables[s] ?? `${varStart}${s}${varEnd}` : s)
  .join('');