symbolToPrimitive.js

class Decimal {
  constructor(number) {
    this.precision = 8
    this.number = number
    this.integer = Math.floor(number)
    this.fractional = Math.round(number * Math.pow(10, this.precision))
  }
  
  [Symbol.toPrimitive](hint) {
    // hint can be: string, number, default
    if (hint === 'string') {
      return `Decimal(${this.number})`
    }
    return this.number
  }
}

const value = new Decimal(7.77)
console.log(`${value}`) // Decimal(7.77)
console.log(`${value * 2}`) // 15.54
console.log(typeof `${value}`) // string