Adding, deleting, modifying, checking, traversing and common methods of javascript array

1. Increase::
   push(item1, item2...)Insert […, item1, item2… ] at the end
   unshift(item1, item2, ...): Insert [ item1, item2… , …] at the beginning
   splice(startIndex, ?deleteCount, item1, item2...): Any position
   concat(?item, ?Array): Insert at the end, return array copy
2. Delete::
   pop()Delete the last element of the array, and return
   shift(): Delete the first element of the array, and return
   slice(startIndex, ?endIndex): Delete the specified area element
   splice(startIndex, ?deleteCount): Delete the specified number of elements at the beginning of the specified area, and return the deleted elements in the form of a list. When deleteCount is greater than the remaining elements, the elements before startIndex are retained.
3. change
   splice(startIndex, ?deleteCount, item1, item2...)
4. Check
   [index]: Out of bounds return undefine
indexOf(item, ?startIndex): search from the beginning, return -1 if not found
   lastIndexOf(item, ?startIndex): search from the end, return -1 if not found
5. Traversal
   for循环
for(let item of array) { }: normal response continue, break, return, Item can not modify the original array
   forEach( (item, index) => { } ): can not respond continue, break, return, Item can not modify the original array
6. Some commonly used methods
   map((value, index, array)=>{})
filter((value, index, array)=>{})
reduce((pre, curr, index, array)=>{}, initValue)
reduceRight((pre, curr, index, array)=>{}, initValue)
find((value, index, array)=>{ return 布尔值 })
findIndex((value, index, array)=>{ return 布尔值 })
keys(), values(), entries(): Return iterator object