• diallows global variables
• silent failures throw error (like NaN = 5)
• throw error when attempt delete undeleteable props
• throw error if all obj prop name not unique
• throw error if function param names not unique
• forbid octal syntax
• for with keyword
• eval not introduce new vars
• forbid delete plain names delete x
• forbid arguments.callee

# References

https://stackoverflow.com/questions/1335851/what-does-use-strict-do-in-javascript-and-what-is-the-reasoning-behind-it