template.js

'use strict'
let html = "<title>{{title}}</title><div>{{content}}</div><div>{{content}}</div><div>{{content}}</div><div>{{content}}</div>"
const data = {
  title:"Test",
  content:"Hello World"
}

for(let k in data) {
  let v = data[k]
  let patten = `{{${k}}}`
  let re = new RegExp(patten,"g");
  html = html.replace(re,v);
}

console.log(html);