Standard object in JS

Standard object in JS
1: Do not use new number (), New Boolean (), New String () to create the wrapper object;
2: Use parseint () or parsefloat () to convert any type to number;
3: Use String () to convert any type to string, or call the ToString () method of an object directly;
4: It is not usually necessary to convert any type to Boolean, because you can write directly if (MyVar) {...} ；
The 5:typeof operator can determine number, Boolean, String, function, and undefined;
6: Determine the array to use Array.isarray (arr);
7: Judge null use MyVar = = = NULL;
8: Determine if a global variable exists with typeof Window.myvar = = = ' undefined ';
9: Inside the function to determine whether a variable exists with typeof MyVar = = = ' undefined '.

Standard object in JS