plus.vs.builder.js

function StringBuilder () {
  this._strings = []
}

StringBuilder.prototype.append = function (str) {
  this._strings.push(str)
}

StringBuilder.prototype.toString = function () {
  return this._strings.join('')
}

console.time('plus')
var str = ''
for (var i = 0; i < 1000000; i++) {
  str += 'text'
}
console.timeEnd('plus')

console.time('builder')
var builder = new StringBuilder()
for (var i = 0; i < 1000000; i++) {
  builder.append('text')
}
console.timeEnd('builder')