> For the complete documentation index, see [llms.txt](https://javascript-1.gitbook.io/javascript/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://javascript-1.gitbook.io/javascript/optimized-code.md).

# Optimized Code

* eval() - window object, we do not call **eval()** to evaluate an arithmetic expression; JavaScript evaluates arithmetic expressions automatically. `Ex: var x = 10; var y = 20; var a = eval("x * y") // 200`
* arguments - in functions
* for in - for looping the objects use object.keys instead
* with - we can access the object properties directly. `Ex: with(Math) { console.log(PI) }; instead using console.log(Math.PI)`
* delete - to delete the object keys `Ex: delete Math.PI;`
* Hidden classes
* Inline caching