前端面试题

2023-11-19

[面试必过][顺利签约][成功上岸][锦鲤附体]

### 数据类型 String、Number、Boolean、null、undefined、Symbol、BigInt、Object

防抖与节流

手写防抖

function debounce(delay,callback) {
  let timer;
  return function(value)  {
    if(timer) clearTimeout(timer);
    timer = setTimeout( function() {
      callback(value)
    }, delay);
  }
}

function throttle(delay,callback) {
  let timer;
  return function() {
    if(!timer) {
      timer = setTimeout(function() {
        callback()
        // 初始化timer
        timer = null;
      },delay)
    }
  }
}

call、apply

Function.prototype.call = function(context) {
  if(typeof context === 'function') {
    throw Error ('call 第一个参数必须是对象')
  }
  
  context = context || windows;
  let args = [...arguments].slice(1)
  context.fn = this;
  delete context.fn
  return context.fn(...args)
}

Function.prototype.apply = function(context) {
  if(typeof context === 'function') {
    throw Error ('apply 第一个参数必须是对象')
  }

  context = context || windows;
  context.fn = this;
  let result;
  if(arguments[1]) {
    result = context.fn(...arguments[1])
  } else {
    result = context.fn()
  }
  delete context.fn
  return result
}

数组去重

function setUnique(arr) {
  return [...new Set(arr)]
}

function indexOfUnique(arr) {
  let newArr = [];
  for(let i = 0; i < arr.length; i++) {
    if(newArr.indexOf(arr[i]) === -1) {
      newArr.push(arr[i])
    }
  }
  return newArr;
}

function includesUnique(arr) {
  let newArray = []
  for(let i = 0; i< arr.length; i++) {
    if(!newArray.includes(arr[i])) {
      newArray.push(arr[i])
    }
  }
  return newArray;
}

function filterUnique(arr)  {
  return arr.filter((item,i,arr) => {
      return arr.indexOf(item, 0) === i
    }
  )
}