常用的前端小知识

JavaScript/前端
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2024-07-03
1.水平垂直居中

两种方式定位或者flex

//定位
div {
    width: 100px;
    height: 100px;
    position: absolute;
    top: 0;
    right: 0;
    bottom: 0;
    left: 0;
    margin: auto;
}
//flex  父级控制子集
.parent {
    display: flex;
    justify-content: center;
    align-items: center;
}
2.css一行文本超出…


overflow: hidden;
text-overflow:ellipsis;
white-space: nowrap;
3. 多行文本超出显示
display: -webkit-box;
-webkit-box-orient: vertical;
-webkit-line-clamp: 3;
overflow: hidden;
4. localStorage


localStorage.name = 'yd';
// 获取
localStorage.name; // yd
// 删除
delete localStorage.name;
// 清除全部
localStorage.clear();
// 遍历
for (let i = 0; i < localStorage.length; i++) {
    const key = localStorage.key(i); // 获取本地存储的Key
    localStorage[key]; // 获取本地存储的value
}
5.防抖


function debounce(fn, delay) {
  let timer
  return function (...args) {
    if (timer) {
      clearTimeout(timer)
    }
    timer = setTimeout(() => {
      fn.apply(this, args)
    }, delay)
  }
}
// 测试
function task() {
  console.log('run task')
}
const debounceTask = debounce(task, 1000)
window.addEventListener('scroll', debounceTask)
6. 节流


function throttle(fn, delay) {
  let last = 0 // 上次触发时间
  return (...args) => {
    const now = Date.now()
    if (now - last > delay) {
      last = now
      fn.apply(this, args)
    }
  }
}

// 测试
function task() {
  console.log('run task')
}
const throttleTask = throttle(task, 1000)
window.addEventListener('scroll', throttleTask)
7. 深拷贝
function deepClone(obj, cache = new WeakMap()) {
  if (typeof obj !== 'object') return obj // 普通类型,直接返回
  if (obj === null) return obj
  if (cache.get(obj)) return cache.get(obj) // 防止循环引用,程序进入死循环
  if (obj instanceof Date) return new Date(obj)
  if (obj instanceof RegExp) return new RegExp(obj)
  
  // 找到所属原型上的constructor,所属原型上的constructor指向当前对象的构造函数
  let cloneObj = new obj.constructor()
  cache.set(obj, cloneObj) // 缓存拷贝的对象,用于处理循环引用的情况
  for (let key in obj) {
    if (obj.hasOwnProperty(key)) {
      cloneObj[key] = deepClone(obj[key], cache) // 递归拷贝
    }
  }
  return cloneObj
}

// 测试
const obj = { name: 'Jack', address: { x: 100, y: 200 } }
obj.a = obj // 循环引用
const newObj = deepClone(obj)
console.log(newObj.address === obj.address) // false
8.promise


class MyPromise {
  constructor(executor) { // executor执行器
    this.status = 'pending' // 等待状态
    this.value = null // 成功或失败的参数
    this.fulfilledCallbacks = [] // 成功的函数队列
    this.rejectedCallbacks = [] // 失败的函数队列
    const that = this
    function resolve(value) { // 成功的方法
      if (that.status === 'pending') {
        that.status = 'resolved'
        that.value = value
        that.fulfilledCallbacks.forEach(myFn => myFn(that.value)) //执行回调方法
      }
    }
    function reject(value) { //失败的方法
      if (that.status === 'pending') {
        that.status = 'rejected'
        that.value = value
        that.rejectedCallbacks.forEach(myFn => myFn(that.value)) //执行回调方法
      }
    }
    try {
      executor(resolve, reject)
    } catch (err) {
      reject(err)
    }
  }
  then(onFulfilled, onRejected) {
    if (this.status === 'pending') {
      // 等待状态,添加回调函数到成功的函数队列
      this.fulfilledCallbacks.push(() => {
        onFulfilled(this.value)
      })
      // 等待状态,添加回调函数到失败的函数队列
      this.rejectedCallbacks.push(() => {
        onRejected(this.value)
      })
    }
    if (this.status === 'resolved') { // 支持同步调用
      console.log('this', this)
      onFulfilled(this.value)
    }
    if (this.status === 'rejected') { // 支持同步调用
      onRejected(this.value)
    }
  }
}

// 测试
function fn() {
  return new MyPromise((resolve, reject) => {
    setTimeout(() => {
      if(Math.random() > 0.6) {
        resolve(1)
      } else {
        reject(2)
      }
    }, 1000)
  })
}
fn().then(
  res => {
    console.log('res', res) // res 1
  },
  err => {
    console.log('err', err) // err 2
  })
9. sort排序


// 对数字进行排序,简写
const arr = [3, 2, 4, 1, 5]
arr.sort((a, b) => a - b)
console.log(arr) // [1, 2, 3, 4, 5]

// 对字母进行排序,简写
const arr = ['b', 'c', 'a', 'e', 'd']
arr.sort()
console.log(arr) // ['a', 'b', 'c', 'd', 'e']
10.Set 去重


cosnt newArr = [...new Set(arr)]