1. console.log('null == 0'); // 'null == 0'
    2. // 比较运算符是会做数据转换, 相等运算符 null 不做数据转换
    3. console.log(null == 0); // false
    4. console.log(null > 0);  // false
    5. console.log(null < 0);  // false
    6. console.log(null >= 0); // true
    7. console.log(null <= 0); // true 
    9. console.log(undefined == 0); // false
    10. console.log(undefined > 0);  // false
    11. console.log(undefined < 0);  // false
    12. console.log(undefined >= 0); // true
    13. console.log(undefined <= 0); // true
    15. console.log(typeof('null == 0')); // string
    17. console.log(typeof(String)); // function
    19. Object.prototype.hello = function(){
    20.   console.log(1111);
    21. }
    23. hello(); // 1111
    25. a > 1 ? console.log(1) : console.log(2); // 报错 a is not defined
    27. conosle.log(name); // ''
    29. typeof(console.log(1 + '1' * '2' / 2 + typeof(name))); // 会打印 2string,返回值是'undefined'
    31. typeof(a); // undefined
    33. // 1.
    34. Array.prototype.slice = function(){
    35.   console.log(aaa); // a is not defined
    36. }
    37. var arr = [].slice();
    38. console.log(arr);  
    40. // 2.
    41. Array.prototype.slice = function(){
    42.   console.log('aaa'); // aaa
    43. }
    44. var arr = [].slice();
    45. console.log(arr); // undefined
    47. // 3. 
    48. Array.prototype.slice = function(){
    49.   console.log('aaa'); // aaa
    50.   return 1;
    51. }
    52. var arr = [].slice(); 
    53. console.log(arr); // 1