by defult javascriot non strict way ma run hota hai.iska mtlb yaha hai ki javascript non strict mood ma kuch error ko ignore kar ta hai.for example:
x = 10;
console.log(x);hum same code ko strict mood ma run kartay hai to error ayagi code strict mood ma run karnay ka leya "use strict" ka use hota hai
use strict ko hama frist line ma use kar na hota hai.