Interview

Interview

二月 10, 2018

Prepare for daocloud

for...in & for...of & forEach

all of them above are used to traverse Object/Array. But these are some difference.

  1. can’t use break or continue in forEach to jump out loop even if you use return. since it does not support.

  1. for…in(use for Object normally)

    • index of Array is type of Number. But index will change and become string in for…in syntax
    • in some case, for...in traverse key without sequence.

  2. for…of(use for Array)

    • can work with break,continue,return
    • cant use for Object
    • use for any structure as long as it have iteration interface

debounce & throttle

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// debounce
let isDebounce = null
document.getElementById('input').oninput = () => {
  isDebounce ? clearTimeout(bounce):''
  isDebounce = setTimeout(() => {
    // code your logic here
  },300)
}

// throttle
let isThrottle = fasle
document.getElementById('input').oninput = () => {
  if(isThrottle) {
    return
  }
  isThrottle = true
  setTimeout(() => {
    // execute logic and change status
    isThrottle = false
  },300)
}

scroll overflow(称为滚动溢出，页面的某块滚动到底后再滚动也不带动整个页面滚动)

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function preventScroll(id) {
  const _this = document.getElementById(id)
  if(navigator.userAgent.indexOf('Firefox') > 0) {
    _this.addEventListener('DOMMouseScroll',event => {
      _this.scrollTop += e.detail > 0 ? 60 : -60 // move 60px every scroll
      event.preventDefault()
    },fasle)
  } else {
    _this.onmousewhell = event => {
      event = event || window.evnet // for IE8-
      _this.scrollTop += event.wheelDelta > 0 ? -60 : 60
    }
}