chipmunkbot3/commands/rainbowify.js

const { literal, argument, greedyString } = require('brigadier-commands')
const colorsys = require('colorsys')

module.exports = {
  register (dispatcher) {
    const node = dispatcher.register(
      literal('rainbowify')
        .then(
          argument('message', greedyString())
            .executes(c => this.rainbowifyCommand(c))
        )
    )

    node.description = 'Makes text rainbow'
    node.permissionLevel = 0
  },

  rainbowifyCommand (context) {
    const source = context.source
    const message = context.getArgument('message')

    const result = []
    let hue = 0
    message.split('').forEach((char) => {
      result.push({ text: char, color: colorsys.hsv2Hex(hue, 100, 100) })
      hue += 355 / Math.max(message.length, 20)
    })

    source.sendFeedback(result, false)
  }
}