modified string builder
string primitive vs object
getElement options
add more about queryselectorall
added underConstruction and other images
Todos under construction
added two more images
Updated perfromance improvement strategy
moved caching example to DOM query
placeholder for caching
two more placeholder
added some junk
added store out of scope variable
moved array forward
best way to create array
added push vs index
careful about index
fromIndex for array indexOf
created array summer
moved array initialize