Edit in JSFiddle

 //JSONオブジェクトを作成
var data1 = {"0":"black","1":"white","2":"red","3":"blue"};
var data2 = {
 "man": {
    "太郎": {
      "fname": "山田",
      "age": 3
     },
    "一郎": {
      "fname": "大和",
      "age": 5
     }
 }
};
      
//JSONからwhiteを取得  
console.log(data1["1"]);
console.log(data2["1"]);
//配列の大きさを求める方法でJSONの大きさを求めてみる
console.log("data1.length => "+data1.length);
console.log("data2.length=> "+data2.length);
//JQueryのsize関数を使ってみる
console.log("$(data1).size()=> "+$(data1).size());
console.log("$(data2).size()=> "+$(data2).size());
//JSONのサイズを表示する
console.log("OK! Object.keys(data1).length => "+Object.keys(data1).length);
console.log("OK! Object.keys(data2['man']).length=> " + Object.keys(data2['man']).length);