entries of fetching iterative method for js array

Directory 1, entires () method syntax details 2. Common use and attention of entires () method 2.1 Return iterator object 2.2 Use of for... of... 2.3 2-dimensional array row sorting

1. Detailed explanation of entires () method syntax

entries() Method returns an iterative object of an array that contains the key-value pairs of the array (key/value) .

The index value of the array in the iteration object is used as the key The array element is used as the value . Its prototype （__proto__:Array Iterator） There is one on the next Method, which can be used to traverse the iterator to get the original array [key,value] . Here, you need to know the knowledge of related iterators.

2. Common use and attention of entires () method

2.1 Returning an Iterator Object

    var arr = ["red", "blue", "green"]
    var x = arr.entries()
    console.log(x); // Array Iterator {}
    console.log(x.next()) //{value: Array:[0, "red"],done:false}
    console.log(x.next()) //{value: Array:[1, "blue"],done:false}
    console.log(x.next()) //{value: Array:[2, "green"],done:false}
    console.log(x.next()) //{value: undefined, done: true}

2.2 Use of for... of...

    const options = [1, , , , 5];
    for (const [index, value] of options.entries()) {
      console.log(value);
    }
    // 0 1
    // 1 undefined
    // 2 undefined
    // 3 undefined
    // 4 5

2.3 2-Dimensional Array Row Sorting

    function sortTwo(arr) {
      var entries = arr.entries()
      var flag = true
      while (flag) {
        var res = entries.next()
        if (!res.done) {
          res.value[1].sort((a, b) => a - b);
          flag = true
        } else {
          flag = false
        }
      }
      return arr
    }
    var arr = [[1, 3, 2], [44, 33], [11, 55, 44, 33]]
    sortTwo(arr)
    console.log(arr);// [[1, 2, 3], [33, 44], [11, 33, 44, 55]]

In the code above, sortTwo Method first gets the iteration object passed into the array, and then defines an initialization ID as true Invoking the iterative object recursively entires Adj. (key/value)0 Method to assign a value to res Object, judgment res Object's d one Property, if the value is true Indicates that it can be recursive, res.value Corresponding to every 1 row of the 2-dimensional array, you can sort the item. If the value is flase Indicates the end of recursion.

Summary: