docsify/src/core/init/lifecycle.js

import { noop } from '../util/core';

export function initLifecycle(vm) {
  const hooks = [
    'init',
    'mounted',
    'beforeEach',
    'afterEach',
    'doneEach',
    'ready',
  ];

  vm._hooks = {};
  vm._lifecycle = {};
  hooks.forEach(hook => {
    const arr = (vm._hooks[hook] = []);
    vm._lifecycle[hook] = fn => arr.push(fn);
  });
}

export function callHook(vm, hook, data, next = noop) {
  const queue = vm._hooks[hook];

  const step = function(index) {
    const hook = queue[index];
    if (index >= queue.length) {
      next(data);
    } else if (typeof hook === 'function') {
      if (hook.length === 2) {
        hook(data, result => {
          data = result;
          step(index + 1);
        });
      } else {
        const result = hook(data);
        data = result === undefined ? data : result;
        step(index + 1);
      }
    } else {
      step(index + 1);
    }
  };

  step(0);
}