BridgeNB

1. Scope is the range where variables are defined and validated. Global scope is the environment 
where variables are available everywhere in this project. 
Local scope is a particular area where variables are vaildated, for example, a function or a file.
2. We have to avoid global variables to aviod misrable bugs.
3. In strict mode, you cannot use a variable without defined it first.
4. Side effects is that one function's output will affect other functions. 
Pure funtion is that this function is both determinate and has no side affect.

BridgeNB

1. https://repl.it/@BridgeNB/Object-creator-drill-2
2. https://repl.it/@BridgeNB/Object-updater-drill-1
3. https://repl.it/@BridgeNB/Self-reference-drill
4. https://repl.it/@BridgeNB/Deleting-keys-drill

BridgeNB

1. https://repl.it/@BridgeNB/Make-student-reports-drill
2. https://repl.it/@BridgeNB/Enroll-in-summer-school-drill
3. https://repl.it/@BridgeNB/find-by-id-drill
4. https://repl.it/@BridgeNB/validate-object-keys-drill

BridgeNB

1. getToken function takes a raw string converted to an array consisted words. 
All words in that array are in lower cases, no punctuations and falsy items,  sorted by alphabetical order.
2. mostFrequentWord function takes a raw string and use getToken to covert it to tokens. 
Then build a dictionary (hash map) to count all words' frequency. Then use a loop to find the most frequent word.