JavaScript: usage of use strict?

we use this string or statement? 

 

Structure of code

 'use strict'; 

We will declare the before any code So here, everything in the file.js will be executed in strict mode.

1. // File Name: mysamplejsfile.js  
2.   
3. 'use strict';  
4. var strcode = 0;  
5. .....  
6. .....  
7. // other code  
8. .....  

Insert this 'use strict'; text on the start of your function body, as shown below. It means that everything in the scope of this function will be executed in strict mode.

1. function sample() {  
2.     'use strict';  
3.     ...  
4.     // other code  
5.     ...  
6. }  

Note

For example, everything will be non-strict except for the function we mark 'use strict' inside the function.