Iteratable object and class arrays

Iteratable object

Realized Iterator Data structure of the interface , Deployed Symbol.Iterator object

Traverse

• while loop

  /** ITERABLE Represents some kind of traversable data structure ,$iterator Is its iterator object .
  Each time the traverser object moves the pointer （next Method ）, Check the return value done attribute , If the traversal is not over , Just move the pointer of the traverser object to the next step （next Method ）, Keep cycling
  */
  var $iterator = ITERABLE[Symbol.iterator]();
  var $result = $iterator.next();
  while (!$result.done) {
   var x = $result.value;
   // ...
   $result = $iterator.next();
  }
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• for...of

Convert to array

• Extension operator

  Extension operator （...） For internal use for...of loop , So it can be used for iteratable objects

  let set = new Set().add('a').add('b').add('c');
  ['a', ...set, 'd'] // ["a", "a", "b", "c", "d"]
  ​
  let map = new Map().set('a', 1).set('b', 2);
  [...map] // [["a", 0], ["b", 1]]
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• Array.from()

  Creates a new object similar to an array or iteratable object , Array instance of shallow copy

  let set = new Set().add('a').add('b').add('c');
  Array.from(set) // ["a", "b", "c"]
  ​
  let map = new Map().set('a', 1).set('b', 2);
  Arrary.from(map) // [["a", 0], [b", 1]]
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An array of class

There are numeric key names and length attribute

Traverse

Convert to array

• Array.from(arrLike)

• Array of slice Method + call/ apply

  let arrLike = {
   0: 'a',
   1: 'b',
   2: 'c',
   length: 3
  };
  ​
  // call change this The direction of
  Array.prototype.slice.call(arrLike)
  arrLike // ["a", "b", "c"]
  // perhaps
  [].slice.call(arrLike)
  arrLike // ["a", "b", "c"]
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