"Use strict"; The correct use of

"Use strict"; When placed in the starting position of a JavaScript file or function (I am not sure if the script tag can begin), you can turn on strict mode. Otherwise-in the case of a JavaScript file that is not at the beginning of the file and not at the beginning of the function-it is a generic string that is not used, except that it wastes a few bytes and is of little use. It is generally recommended to add "use strict" at the beginning of all functions (or all outermost functions); The command starts strict mode, and it is never recommended to write the global "use strict" at the beginning of the file-instead, some ES validators give a warning.

Global "use strict" why not? One important reason is that when a file is merged, some files are in strict mode, while others are not. At this time these are the strict mode of the file, the merge, the string to the middle of the file, not only does not indicate strict mode, but in the compression after the waste of bytes.

Excerpted from http://www.guokr.com/post/534018/

"Use strict"; The correct use of