indexed database IndexedDB

Indexed Database API 目的是提供一个可供javascript存储和检索对象，并且还能进行查询，搜索等数据库操作

设计为几乎完全异步，因此绝大部分操作都稍后执行，因此每次操作都应该提供onerror和onsuccess来处理结果

目前还没有完全支持，因此：var indexedDB = window.indexedDB || window.msIndexedDB || window.mozIndexedDB || window.webkitIndexedDB;

IndexedDB 和MySQL最大的区别在于用对象存储而不是表格来记录数据

const dbName = "the_name";

var request = indexedDB.open(dbName, 2);

request.onerror = function(event) {
  // Handle errors.
};
request.onupgradeneeded = function(event) {
  var db = event.target.result;

  // Create an objectStore to hold information about our customers. We‘re
  // going to use "ssn" as our key path because it‘s guaranteed to be
  // unique.
  var objectStore = db.createObjectStore("customers", { keyPath: "ssn" });

  // Create an index to search customers by name. We may have duplicates
  // so we can‘t use a unique index.
  objectStore.createIndex("name", "name", { unique: false });

  // Create an index to search customers by email. We want to ensure that
  // no two customers have the same email, so use a unique index.
  objectStore.createIndex("email", "email", { unique: true });

  // Use transaction oncomplete to make sure the objectStore creation is
  // finished before adding data into it.
  objectStore.transaction.oncomplete = function(event) {
    // Store values in the newly created objectStore.
    var customerObjectStore = db.transaction("customers", "readwrite").objectStore("customers");
    for (var i in customerData) {
      customerObjectStore.add(customerData[i]);
    }
  }};