//創(chuàng)建ajax通信服務(wù)器對(duì)象

function getHTTPObject(){

  "use strict"; //注意使用嚴(yán)格模式

  var xhr;

  //使用主流的XMLHttpRequest通信服務(wù)器對(duì)象

  if(window.XMLHttpRequest){

    xhr = new window.XMLHttpRequest();

  //如果是老版本ie，則只支持Active對(duì)象
  } else if(window.ActiveXObject){

    xhr = new window.ActiveXObject("Msxml2.XMLHTTP");
  }

  //將通信服務(wù)器對(duì)象返回
  return xhr;

}

//ajax JSON Salad
var ingredient = {
  "fruit":[
    {
      "name" : "apple",
      "color" : "green"
    },
    {
      "name" : "tomato",
      "color" : "red"
    },
    {
      "name" : "peach",
      "color" : "pink"
    },
    {
      "name" : "pitaya",
      "color" : "white"
    },
    {
      "name" : "lettuce",
      "color" : "green"
    }
  ]
};

//輸出ajax調(diào)用所返回的json數(shù)據(jù)

var request = getHTTPObject();

request.onreadystatechange = function(){

  "use strict";

    //當(dāng)readyState全等于“4”狀態(tài)，status全等于“200”狀態(tài) 代表服務(wù)器狀態(tài)服務(wù)及客戶(hù)端請(qǐng)求正常，得以返回
  if(request.readyState ===4 || request.status ===200 ){
    
    //為了方便起見(jiàn)，將數(shù)據(jù)打印到瀏覽器控制臺(tái)（F12查看）
    console.log(request.responseText);
  }
  
  //使用GET方式請(qǐng)求.json數(shù)據(jù)文件，并且不向服務(wù)器發(fā)送任何信息
  request.open("GET","data/ingredient.json",true);
  request.send(null);
};

//將其封裝成一個(gè)供調(diào)用函數(shù)

function ajaxCall(dataUrl,outputElement,callback){
  "use strict";  //這是一段截取的js（ajax）代碼

  var request = getHTTPObject();
  //我想要提醒大家的是：當(dāng)網(wǎng)頁(yè)的某個(gè)區(qū)域在向服務(wù)器發(fā)送http請(qǐng)求的過(guò)程中，要有一個(gè)標(biāo)識(shí)提醒用戶(hù)正在加載...

  outputElement.innerHTML = "Loding..."; //也可以根據(jù)各位的需求添加一個(gè)循環(huán)小動(dòng)畫(huà)

  request.onreadystatechange = function () {

    if(request.readyState ===4 || request.status ===200){

      //將request.responseText返回的數(shù)據(jù)轉(zhuǎn)化成JSON格式
      var contacts = JSON.parse(request.responseText);
      
      //如果回調(diào)函數(shù)是function類(lèi)型，則使用callback函數(shù)處理返回的JSON數(shù)據(jù)
      if(callback === "function"){
        callback(contacts);
      }
    }
  };

  request.open("GET","data/ingredient.json",true);
  request.send(null);
}

//調(diào)用程序，我們將使用Ajax請(qǐng)求的JSON數(shù)據(jù)顯示到HTML文檔的某個(gè)區(qū)域中！
(function () {
  "use strict";

    //下面將給出DOM語(yǔ)句相對(duì)應(yīng)的HTML代碼
  var searchForm = document.getElementById("search-form"),
    searchField = document.getElementById("q"),
    getAllButton = document.getElementById("get-all"),
    target = document.getElementById("output");

  var search = {

    salad : function(event){

      var output = document.getElementById("output");
        //請(qǐng)求的JSON數(shù)據(jù)文件名，輸出到HTML的區(qū)域，檢索數(shù)據(jù)文件的核心function語(yǔ)句

      ajaxCall('data/ingredient.json','output',function(data){

        //searchValue為搜索條目，準(zhǔn)備循環(huán)檢索
        var searchValue = searchField.value,

          //找到食材條目（詳見(jiàn)JSON數(shù)據(jù)文件）
          fruit = data.fruit,

          //統(tǒng)計(jì)水果的數(shù)量
          count = fruit.length,
          i;

        //阻止默認(rèn)行為
        event.preventDefault();

        //初始化
        target.innerHTML = "";

        if(count > 0 || searchValue !==""){
          for(i = 0;i < count;i++){
            
            var obj = fruit[i],
              //將name與searchvalue值相匹配，如果值不等于 -1，那么就確定兩者相匹配

              inItfount = obj.name.indexOf(searchValue);

            //將JSON中匹配的數(shù)據(jù)規(guī)范的寫(xiě)入到DOM
            if(isItfount != -1){
              target.innerHTML += '<p>'+obj.name+'<a href="mailto:" '+obj.color+'>'+obj.color+'</a></p>'
            }
          }
        }
      })
    }
  };
  //事件監(jiān)聽(tīng)器，監(jiān)聽(tīng)鼠標(biāo)單擊事件后調(diào)用函數(shù)并請(qǐng)求JSON數(shù)據(jù)文件
  searchField.addEventListener("click",search.salad,false);
  
})();

<h1>制作沙拉所需要的食材</h1>

  <form action="" method="get" id="search-form">

    <div class="section">

      <label for="q">搜索食材</label>
      <input id="q" name="q" required placeholder="type a name">
    </div>


    <div class="button-group">

      <button type="submit" id="btn-search">搜索</button>
      <button type="button" id="get-all">get all contacts</button>

    </div>

  </form>

  <div id="output"></div>