The elements in an array composed of JSON objects are completely deleted in JS

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In JS, for an array consisting of a JSON object, for example:

var test = [{"A": "1", "B": "2"}, {"A": "3", "B": "4"}, {"A": "5", "B": "6"}];

What should we do if we want to delete the second JSON object? In fact, the method is exactly the same as the operation array.

At the beginning of the attempt to use the delete operator, but when querying the length of the array, it is found that this method does not completely delete the element, but instead deletes its value, but still retains space.

    var test = [{"A": "1", "B": "2"}, {"A": "3", "B": "4"}, {"A": "5", "B": "6" }];    Test.length   // output is 3    Delete test[1];    Test.length   // output is still 3

Query operator Delete We know that it simply resets the value to undefined without affecting the length of the array, turning it into a sparse array ("JS authoritative guide" section 7.5).

To understand this, perhaps think of the deletion point after the elements can be moved forward 1 units, the implementation of the total elimination of the element, but in the JS method we can find a more convenient way: Splice () method

    var test = [{"A": "1", "B": "2"}, {"A": "3", "B": "4"}, {"A": "5", "B": "6" }];    Test.length   // output is 3    test.splice (1, 1);    Test.length   // output is 2

Test.length becomes 2 after deletion, which is exactly what we want.

We can find a description of the splice () in the information about:

arrayobject.splice (Index, Howmany, Item1, ..., ItemX) method adds/Deletes an item to/from the array, and then returns the item that was deleted.

Parameter 1:index is the starting position for insert additions or (and) deletions;

Parameter 2:howmany Specifies the number of elements added/removed from the array;

Parameter 3:item1, ..., ItemX Optional, select the Add action to fill in, indicating the element that needs to be added.

The elements in an array composed of JSON objects are completely deleted in JS