Method add

lib/lazy-result.js:250–253

(plugin, type, cb)

  prepareVisitors() {
    this.listeners = {}
    let add = (plugin, type, cb) => {
      if (!this.listeners[type]) this.listeners[type] = []
      this.listeners[type].push([plugin, cb])
    }
    for (let plugin of this.plugins) {
      if (typeof plugin === 'object') {
        for (let event in plugin) {