Class to generate random number.

generator.js

export class Generator {
  // constructor (private readonly len: number = 6) {}
  len: number = 10

  randomNumber (): string {
    return Math.floor(
      Math.pow(10, this.len - 1) +
          Math.random() * (Math.pow(10, this.len) - Math.pow(10, this.len - 1) - 1)
    ).toString()
  }

  randomString (): string {
    let randomString = ''
    const charSet = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz'
    for (let i = 0; i < this.len; i += 1) {
      const randomPoz = Math.floor(Math.random() * charSet.length)
      randomString += charSet.substring(randomPoz, randomPoz + 1)
    }
    return randomString
  }

  getPrefix (length: number = NaN): string {
    const charSet = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz'
    this.len = !isNaN(length) ? length : this.len

    return Array.apply(null, Array(this.len))
      .map(() => {
        return charSet.charAt(Math.floor(Math.random() * charSet.length))
      })
      .join('')
  }

  /**
     * Generate 6 digits token
     */
  generateToken (): string {
    const dateTime = new Date()
    return (Math.floor(dateTime.getTime() * 90000) + 10000).toString().substring(8, 14)
  }

  generateOtp (): string {
    return `${this.getPrefix(3)}${this.generateToken().substring(2, 6)}`
  }
}