var a = 1;
function test() {
 var a = 2;
 console.log(a); // 2
}
test();

var a = 1;
function test2() {
 console.log(a); // undefined
 var a = 2;
}
test2();

var a = 1;
function test3() {
 console.log(a); // 1
 a = 2;
}
test3();

let b = 1;
function test4() {
 console.log(b); // b is not defined
 let b = 2;
}
test4();

function test5() {
 let a = 1;
 {
  let a = 2;
 }
 console.log(a); // 1
}
test5();

var arr = [],
 arr2 = [1];
console.log(arr === arr2); // false

var arr = [],
 arr2 = [];
console.log(arr === arr2); // false

var arr = [],
 arr2 = {};
console.log(typeof(arr) === typeof(arr2)); // true

var arr = [];
console.log(arr instanceof Object); // true
console.log(arr instanceof Array); // true

var obj = {
 name: 'xiaoming',
 getName: function () {
  return this.name
 }
};
console.log(obj.getName()); // 'xiaoming'

var obj = {
 myName: 'xiaoming',
 getName: function () {
  return this.myName
 }
};
var nameFn = obj.getName;
console.log(nameFn()); // undefined

var obj = {
 myName: 'xiaoming',
 getName: function () {
  return this.myName
 }
};
var obj2 = {
 myName: 'xiaohua'
};
var nameFn = obj.getName;
console.log(nameFn.apply(obj2)); // 'xiaohua'

function test6() {
 console.log(arguments); // [1, 2]
}
test6(1, 2);

function test7 () {
 return function () {
  console.log(arguments); // 未执行到此，无输出
 }
}
test7(1, 2);

var args = [1, 2];
function test9() {
 console.log(arguments); // [1, 2, 3, 4]
}
Array.prototype.push.call(args, 3, 4);
test9(...args);

var elem = document.getElementsByTagName('div'); // 如果页面上有5个div
for(var i = 0; i < elem.length; i++) {
 elem[i].onclick = function () {
  alert(i); // 总是5
 };
}

var elem = document.getElementsByTagName('div'); // 如果页面上有5个div
for(var i = 0; i < elem.length; i++) {
 (function (w) {
  elem[w].onclick = function () {
   alert(w); // 依次为0,1,2,3,4
  };
 })(i);
}

var obj = {
 name: 'xiaoming',
 age: 23
};
var newObj = obj;
newObj.name = 'xiaohua';
console.log(obj.name); // 'xiaohua'
console.log(newObj.name); // 'xiaohua'

var obj2 = {
 name: 'xiaoming',
 age: 23
};
var newObj2 = Object.assign({}, obj2, {color: 'blue'});
newObj2.name = 'xiaohua';
console.log(obj2.name); // 'xiaoming'
console.log(newObj2.name); // 'xiaohua'
console.log(newObj2.color); // 'blue'

var obj3 = {
 name: 'xiaoming',
 age: 23
};
var newObj3 = Object.create(obj3);
newObj3.name = 'xiaohua';
console.log(obj3.name); // 'xiaoming'
console.log(newObj3.name); // 'xiaohua'