一、另类排序

题目：

/**
 * 1. 排序后输出 id
 * @param {Array<Object>} list
 * @returns {Array<number>}
 * @example
 * [
 *  { id: 2, before: 1 },
 *  { id: 1, last: true },
 *  { id: 3, after: 1 },
 *  { id: 5, first: true },
 *  { id: 6, last: true },
 *  { id: 7, last: true },
 *  { id: 8, last: true },
 * ];
 * 输出为
 * [5, 2, 1, 3, 6, 7, 8];
 * [
 * 	{ id: 2, before: 3 },
 *	{ id: 1, before: 2 },
 *	{ id: 3, before: 5 },
 *  { id: 5, before: 6 },
 *	{ id: 6, last: true },
 * 	{ id: 7, last: true },
 * 	{ id: 8, last: true },
 * ];
 * 输出：
 * [1,2,3,5,6,7,8]
 */

解法1：

 function sort(source, target = []) {
  if (source.length === 0) {
      return target
  }
  const current = source.shift()

  const { id, before, after, first, last  } = current

  if (first) {
      target.unshift(id)
  }

  if (last) {
      target.push(id)
  }

  /**
   * 前后关系处理，找到对应的index，如果对应的目标未入盏则放到最后进行处理
   */
  if ('before' in current || 'after' in current) {
      const targetId = before || after
      const index = target.findIndex(value => value === targetId)
      if (index === -1) {
          
          /**
           * source 和 target都不存在目标id的情况下，直接插入
           */
          if (source.find(value => value === targetId)) {
              source.push(current)
              return sort(source, target)
          } else {
              target.push(id)
          }

      } else {
          target.splice('before' in current ? index : index + 1, 0, id)
      }
  }

  return sort(source, target)
}

解法2：

function parse(list) {
  let result = [];
  let filtered = [];
  for(let i of list){
    if(i.first){
      result.unshift(i.id);
    }else if(i.last){
      result.push(i.id);
    }else{
      filtered.push(i);
    }
  }

  while(filtered.length){
    let cur = filtered.shift();
    let key = cur.before ? cur.before : cur.after;
    let index = result.findIndex(i=>i===key);
    if(index !== -1){
      result.splice(cur.before ? index: index+1,0,cur.id);
    }else{
      filtered.push(cur);
    }

  }
}

二、二维数组转树状结构

题目：

/**
 * 2. 将数组转换成树状结构
 * @param {Array} arr
 * @returns {Object}
 * @example
 * [
 *   { id: 1, name: 'i1' },
 *   { id: 2, name: 'i2', parentId: 1 },
 *   { id: 4, name: 'i4', parentId: 3 },
 *   { id: 3, name: 'i3', parentId: 2 },
 *   { id: 8, name: 'i8', parentId: 7 },
 * ]
 * 转换后
 * {
 *   id: 1,
 *   name: 'i1',
 *   children: [
 *     { id: 2, name: 'i2', parentId: 1, children: [...] },
 *   ]
 * }
 */

解答：

function convert2Tree(arr) {
	let parentMap = {};
	let root;
	arr.sort((a,b)=>a.id-b.id);

	for(let node of arr){
		node.children = [];
		if(!node.parentId){
			
			root = node;
			
		}else{
			let parent = parentMap[node.parentId];
			if(parent){
				parent.children.push(node);
			}
			
		}
		parentMap[node.id] = node;
	}
	return root;
}

三、用setTimeout实现setInterval

/**
 * 3. 实现 setInterval
 * 利用 setTimeout 实现 setInterval
 * 利用 clearTimeout 实现 clearInterval
 */

/**
 * @param {Function} callback
 * @param {number} duration
 * @returns {number}
 * @example
 * mySetInterval(()=> {
 *   console.log('xxx');
 * }, 200);
 */
let timerMap = {};
let id = 0;
function mySetInterval(callback, duration) {
	let timerId = id;
	id++;
	function fn(){
		callback();
		timerMap[timerId] = setTimeout(()=>{
			fn();
		}, duration)
	}
	timerMap[timerId] = setTimeout(fn, duration);
	return timerMap[timerId];
}

/**
 * @param {number} timer
 * @returns {void}
 * @example
 * const timer = mySetInterval(()=> {
 *   console.log('xxx');
 * }, 200);
 * setTimeout(() => {
 *   myClearInterval(timer);
 * }, 1000);
 */
function myClearInterval(timer) {
	clearTimeout(timerMap[timer]);
	// clearTimeout(timer);
	delete timerMap[timer];

}

参考