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How-to-implement-auto-complete.md

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title comments date type categories tags
How to implement auto-complete?
true
2018-10-08 13:13:10 -0700
categories
Full stack
auto-complete
event delegation
debounce
cache

I. Logic

  1. For each input, wait 500ms to make API call, to load 40 items
  2. scroll down close to bottom ( less than 20px left ), make API call to load another 40 items
  3. could add local cache, to speed up response

II. code

  1. <!DOCTYPE html>
<html>
<head>
<style>
#wrapper {
    margin-top: 10px;
    overflow: auto;
    width: 250px;
    display: inline-block;
    border: 1px solid red;
    overflow: hidden;
}

.listWrapper{
	border: 1px solid blue;
    height: 200px;
    width: 140px;
    overflow: auto;
    scroll: auto;
}

</style>
</head>
<body>
<div id="wrapper">
  <div>
      <input id="inputText" /> 
      <button>submit</button>
  </div>
</div>

<script>
	
    let body = document.getElementsByTagName("BODY")[0]
    let data = Array.from({length: 40}, () => "recommdation"+Math.floor(Math.random() * 40));
    
	const API = "https://www.demo.com/potentialList"
    let isFetching = false  // used for scroll
    let isEnd = false		// used for scroll
    
    
    // create new element below <input> inside div wrapper. For both 'input' & 'scroll'
    function appendList(elementCollection, wrapper, isScroll){
        if(isScroll){
        	let listWrapper = document.getElementsByClassName("listWrapper")[0]
            data.forEach( ele=>{
                let itemNode = document.createElement("DIV")
                let textNode = document.createTextNode(ele)
                itemNode.appendChild(textNode)
                listWrapper.appendChild(itemNode)
            })
            return
    	}
        
        let oldlistWrapper = document.getElementsByClassName("listWrapper")
        if(oldlistWrapper.length > 0){
          wrapper.removeChild(oldlistWrapper[0])
        }
    	let listWrapper = document.createElement("DIV")
    	listWrapper.setAttribute("class", "listWrapper")
    	let list = Array.prototype.slice.call(elementCollection)
        data.forEach( ele=>{
            let itemNode = document.createElement("DIV")
            let textNode = document.createTextNode(ele)
            itemNode.appendChild(textNode)
            listWrapper.appendChild(itemNode)
        })
        listWrapper.addEventListener("click", putToInput)
        listWrapper.addEventListener("scroll", scrollHandler)
        wrapper.appendChild(listWrapper)
        
    }
    
    
    // onclick callback for items provided
    function putToInput(e){
    	let input = document.getElementById("inputText")
    	let wrapper = document.getElementById("wrapper")
    	let listWrapper = document.getElementsByClassName("listWrapper")[0]
        input.value = e.target.innerHTML
        console.log(e.target)
        wrapper.removeChild(listWrapper)
    }
    
    
    // make API call
    function makeAPICall(API, val, isScroll){
      console.log("val: ", val)
      // 1. first check local cache
        
      // 2. hit fail, call API
      let ajax = new XMLHttpRequest()
      ajax.open("GET", "https://www.w3schools.com/js/ajax_info.txt", true)
      ajax.onreadystatechange = function(){
        if(this.readyState === 4 && this.status === 200 ){
          console.log(this.responseText)
          let parser = new DOMParser()
          let a = parser.parseFromString(this.responseText, "text/html")
          console.log(a)
          let body = a.getElementsByTagName("BODY")[0]
          let wrapper = document.getElementById("wrapper")
          if(val.localeCompare("scroll made request")===0){
          	isFetching = false
          }
          appendList(data, wrapper, isScroll)
        }
      }
      ajax.send()
    }
    
    // scroll handler for listWrapper
    function scrollHandler(e){
    	let listWrapper = e.target
        let boxHeight = listWrapper.clientHeight
        let scrollTop = listWrapper.scrollTop
        let scrollHeight = listWrapper.scrollHeight
        
        let remainder = scrollHeight - scrollTop
        let diff = remainder - boxHeight
        console.log("box height: ", boxHeight)
        console.log("scrollTop: ", scrollTop)
        console.log("scrollHeight: ", scrollHeight)
        console.log("diff: ", diff)
        
        if( diff < 20 && !isFetching && !isEnd ){
        	isFetching = true
        	makeAPICall(API, "scroll made request", true)
        }
    }
    
	// debounce 500ms to make API call
    let timeHandler = null
    function inputHandler(e){
    	clearTimeout(timeHandler)
        let val = e.target.value
    	timeHandler = setTimeout( function(){makeAPICall(API, "keypress made request", false)} ,500 )
    }
    
	let input = document.getElementById("inputText")
    addEventListener("input", inputHandler)
</script>

</body>
</html>