I had an idea for a fluent toaster api.

aura-toaster.js

(function Toaster() {
  let mode = 'dismissible'

  const setMode = newMode => {
    mode = newMode
  }

  const fireToast = (title, message, iconName, styleType) => {
    console.log('begin fire mode', mode)
    const toast = $A.get("e.force:showToast")
    toast.setParams({
      title: title,
      message: message,
      key: iconName,
      type: styleType,
      mode
    })
    toast.fire()
    mode = 'dismissible'
    console.log('after fire mode', mode)
  }

  const error = (title, message) => {
    fireToast(title, message, "error", "error")
  }

  const info = (title, message) => {
    fireToast(title, message, "info_alt", "info")
  }

  const success = (title, message) => {
    fireToast(title, message, "success", "success")
  }

  const warning = (title, message) => {
    fireToast(title, message, "warning", "warning")
  }

  const sticky = () => {
    setMode('sticky')
    return toaster
  }

  const pester = () => {
    setMode('pester')
    return toaster
  }

  const toaster = {
    sticky,
    pester,
    error,
    info,
    success,
    warning,
  }

  return toaster
})()

usage.js

toaster.success('title', 'message') // => default success toast
toaster.info('title', 'message') // => default info toast
toaster.sticky().error('title', 'message') // => sticky error toast
toaster.pester().warning('title', 'message') // => pester warning toast