Performance of Arrays and Objects

• Understand how objects and arrays work, through the lens of Big O
• Explain why adding elements to the beginning of an array is costly
• Compare and contrast the runtime for arrays and objects, as well as built-in methods.

When to use objects

• When you don't need order
• When you need fast access / insertion and removal

Big O of Objects

• Insertion $O(1)$
• Removal $O(1)$
• Searching $O(n)$
• Access $O(1)$
• Object.keys $O(n)$
• Object.values $O(n)$
• Object.entries $O(n)$
• hasOwnProperty $O(1)$

When to use Arrays

• When you need order
• When you need fast access / insertion and removal (sort of)

Big Of of Arrays

• Insertion: it depends
• Removal: it depends
• Searching: $O(n)$
• Access: $O(1)$
• Array.push $O(1)$
• Array.pop $O(1)$
• Array.shift $O(n)$
• Array.unshift $O(n)$
• Array.concat $O(n)$
• Array.slice $O(n)$
• Array.splice $O(n)$
• Array.sort $O(n\log{n})$
• Array.forEach Array.map Array.filter Array.reduce $O(n)$