Differences between JavaScript hook and slice, Map and Foreach, Filter(), Reduce()

map and forch

  • Parameters: all(current value, current matching index, currently calling array)
  • I can’t write everything

a map

  • According to the transformation of each element, a new matrix is ​​formed
  • The original group has not changed.
  • Return to a new group

Note the question written: See callback function

[1 "," 2 "," 3 "]. Map (parseint); // Результат [1, NAN, NAN]

for every

  • Through the callback function, perform some operations on each element
  • No return, not specified
  • Poor performance, far from being directly usable, accessing each element with an index

filter and reduce


  • Through True / False of return, filter the elements of the array
  • That’s right: reserve
  • invalid: delete
  • Finally, a new array is returned and the original array will not be modified

scale down

  • Another option, a total of four
  • Prevalue: The first parameter, returning from the previous element
  • The last three parameters are the same as the other parameters
  • Finally returns one value

Paste and slice

splicing (sewing)

  • Used to remove + add
  • Index: Kai started the remote index
  • NUM: number of removes (0 not removed)
  • To add an element, separate it with a comma; add to index center,
  • Modify the original array and return the set of the deleted elements

slice (slice)

  • Used to return specific items
  • start: start pointer (the negative number is counted from the tail, -1 indicates the penultimate one) (do not write from start to end)
  • end: index of the end (no default character for the end)
  • Return a new matrix without changing the original matrix


От: https://www.wolai.com/mary/4d3HuSKg2c4K3CHnDDWkYt

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