Array-Methods

Question 1

isArray

Answer 1

Array.isArray(mixed value)
=>  {bool} test
#ES5

Question 2

pop

Answer 2

.pop()
=>  {mixed} removes & returns last array element; if array is empty, returns undefined
#mutator
#safe

Question 3

push

Answer 3

.push(mixed value1, ... )
=>  {num} new .length after adding values to end of array
#mutator
#safe

Question 4

reverse

Answer 4

.reverse()
=>  {arr-ref} reverses order of array, then returns a reference to itself
#mutator
#safe

Question 5

shift

Answer 5

.shift()
=>  removes & returns first array element; or returns undefined if array is empty
#mutator
#safe

Question 6

sort

Answer 6

.sort(func compare=unicode-point-values)
=>  {arr-ref} sorts array, then returns reference to itself
#mutator
#safe

compare

• arguments (a, b)
  
  • if > 0 returned, a > b
  • if < 0 returned, a < b
  • if 0 returned, a == b
• if omitted, converts every element into a string & uses Unicode point values (16 bit number representing character)

Question 7

unshift

Answer 7

.unshift(mixed value1, ... )
=>  {num} new .length after adding values to front of array
#mutator
#safe

Question 8

concat

Answer 8

.concat(mixed value1, ...)
=>  {arr} new array from primary + value1 + ...
#accessor
#safe
#shallow-copy - meaning reference types have their references copied, so both old and new arrays point to same reference

value
- single values or array becomes the same dimension:
[1, 2].concat([3, 4], 5, [[6]]) => [1, 2, 3, 4, 5, [6]]

Question 9

join

Answer 9

.join(str glue=',')
=>  {str} array glued together into string
#accessor
#safe

glue
- if not string, converted into one

Question 10

slice

Answer 10

.slice(num start=0, num end=length)
=>  
#accessor
#safe
#shallow-copy

start/end
- if < 0, s/e=length+s/e

Question 11

toString

Answer 11

.toString()
=>  {str} array in string form; identical to .join()
#accessor
#safe - but ES5 uses .join() instead of .toString()

Question 12

indexOf

Answer 12

.indexOf(mixed searchValue, num start=0)
=>  {num} first index w/ matching value, else -1
#accessor
#ES5

start

• if < 0, start=length+start
• if > length, returns -1 (not found)

Question 13

lastIndexOf

Answer 13

.lastIndexOf(mixed searchValue, num start=length)
=>  {num} last index w/ matching value, else -1
#accessor
#ES5

start

• the array is search backwards, so if >= length, whole array is searched
• if < 0, start=length+start (offset @ end of array), so -2 would skip thelast 2 elements in the array

Question 14

forEach

Answer 14

.forEach(func iter, obj this=default-this)
=>  {undefined}
#iterator
#ES5
# note - you can't break a .forEach loop, so use .some(return true) or .every(return false) if breaking is needed.

iter
- args: value, index, array

Question 15

every

Answer 15

.every(func iter, obj this=default-this)
=>  {bool} iterates each element until false is returned, causing .every to return false, else returns true.
#iterator
#ES5

iter
- args: value, index, array

Question 16

some

Answer 16

.some(func iter, obj this=default-this)
=>  {bool} iterates each element until true is returned, causing .some to return true, else returns false.
#iterator
#ES5

iter
- args: value, index, array

Question 17

filter

Answer 17

. filter(func iter, obj this=default-this)
=>  {arr} creates a new array containing the elements who's iteration returned true
#iterator
#ES5

iter
- args: value, index, array

Question 18

map

Answer 18

.map(func iter, obj this=default-this)
=>  {arr} creates a new array containing the *values* returned from each iteration
#iteration
#ES5
#note - iteration called on element when value !== undefined

iter
- args: value, index, array

Question 19

reduce

Answer 19

.reduce(func iter, mixed initial-value)
=>  {mixed} each iteration receives the value returned from the previous iteration, until the loop ends and the last returned value is what .reduce returns.
#iterator
#ES5

iter
- args: prevValue, arrValue, index, arr

initial-value !! READ CAREFULLY !!

• if you do NOT provide an initial value, the first iteration will be the first element as prevValue and the second element as arrValue
  
  • it makes sense if you’re trying to pluck a single value from an array, which you’d usually initialize as the first value

Question 20

reduceRight

Answer 20

.reduceRight(func iter, mixed initial-value)
=>  {mixed} same as .reduce but loops from last to first
#iterator
#ES5