JavaScript căn bản - part 2

1. JavaScript Array splice() Method

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Definition and Usage

The splice() method adds/removes items to/from an array, and returns the removed item(s).

Note: This method changes the original array.

Syntax

array.splice(index, howmany, item1, ....., itemX)

Parameter Values

Parameter	Description
index	Required. An integer that specifies at what position to add/remove items, Use negative values to specify the position from the end of the array
howmany	Optional. The number of items to be removed. If set to 0, no items will be removed
item1, ..., itemX	Optional. The new item(s) to be added to the array

Return Value:	A new Array, containing the removed items (if any)

Example

At position 2, add the new items, and remove 1 item:

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.splice(2, 1, "Lemon", "Kiwi");

=> result = Banana,Orange,Lemon,Kiwi,Mango

Example

At position 2, remove 2 items:

var fruits = ["Banana", "Orange", "Apple", "Mango", "Kiwi"];
fruits.splice(2, 2);

Example

At position 2, remove 0 items and add 2 items:

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.splice(2, 0, "abc" , "Kiwi");

=> result = [Banana,Orange,abc,Kiwi,Apple,Mango]

2. valueOf() Method

Return the primitive value of a string object:

<script>
function myFunction() {
    var str = "Hello World!";
    var res = str.valueOf();
    document.getElementById("demo").innerHTML = res;
}
</script>

3. Set and Map

Set:

mySet[Symbol.iterator]

Return value

The Set iterator function, which is the values() function by default.

Example:
vm.fileSetUpload = new Set();
var rmID = $('#btnRemoveSetupFileSrv').val();
vm.fileSetUpload.add(rmID.valueOf());
const iterator1 = vm.fileSetUpload[Symbol.iterator]();
vm.arrRmAttachFile = [];
for (var v of vm.fileSetUpload) {
    vm.arrRmAttachFile.push(v);
}         

Map:
vm.filesMapUpload = new Map();
for (var i = 0; i < e.length; i++) {
    vm.filesMapUpload.set(e[i].name, e[i]);
   
}
var fNames = '';
vm.filesMapUpload.forEach(function(value, key, map) {
    fNames = fNames + key + ":";
});

var rmID = $('#btnRemoveSetupFileCli').val();
vm.filesMapUpload.delete(rmID);

vm.filesArrayUpload = [];
vm.filesMapUpload.forEach(function(value, key, map) {
       vm.filesArrayUpload.push(value);
});

4.Reduce method

The reduce() method executes a reducer function (that you provide) on each element of the array, resulting in a single output value.

link:
https://www.freecodecamp.org/news/reduce-f47a7da511a9/
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/reduce

5.Array.prototype.map()

The map() method creates a new array populated with the results of calling a provided function on every element in the calling array.


REF:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/map