Arrays in JavaScript

Basic Syntax:


    var arrayName = [item0, item1, item2];

An Array can contain multiple types of items

An Array can have an Array as an item.


    var Array = ['string1', 5 , [0,1,2], true]


    var nums = [1, 1, 2, 3, 5, 8, 13, 21]
    for ( var i = 0 ; i < nums.length; i++) {
        console.log('in position ' + i + ' there is : ' + nums[i]);
    }


    in position 0 there is : 1
    in position 1 there is : 1
    in position 2 there is : 3
    in position 3 there is : 5
    in position 4 there is : 8
    in position 5 there is : 13
    in position 6 there is : 21

Array with various types


var Array1 = 
[
    'someString',                   //text
    5 ,                             //number
    [ 0, 'oneMoreString', 2],       //array (with multiple types)
    true,                           //boolean
    { name: 'Guy', age: 46}         //object with 2 childs
]

Assignment and additions


Array1[1] = 7;                      //Addition to the array
Array1[4].lastName = 'Maimon';      //addition to the Object
Array1[Array1.length] = [3,4,5,6];  //Addition of an Array to the end
And then 

console.log(Array1[Array1.length-1]);
Will result

    [3, 4, 5, 6]
the last item in the main array And

console.log(Array1[Array1.length-1][Array1[Array1.length-1].length-1]);
Will result

    6
which is the last item in the internal array inside the main array

Arrays useful methods in JavaScript

Array.forEach


    arr.forEach(function(theItems, myArrIndex, myArr){}


The Arguments in the function are:
The 1st will return the Items of the Array
The 2nd will return the index of each Items
the 3rd will return the array

Add on or more items to the end of an array


    arr.push(item,item);

Delete the last item of an array


    arr.pop();

To remove all the items from an array


    for (i= 0 ; i < arr.length ; i) {      //No Increment needed!!!
        arr.pop();
    }
Or

while (arr.length >0) {
    arr.pop();
}
pop() also returns the removed item

    removedItem = arr.pop();
Will return the removed item and assign it to the variable

Add an item to the beginning of an array


    arr.unshift(item)

check for place of item in an array

arr.indexOf(item)
will return the 0 based location of an item, if not exist, will return -1

remove multiple items from an array (not last)


arr.splice(startingIntem,NumOfItems);
like pop(), returns the removed item(s) as an variable or array

CAUTION: 
if startingNumber smaller than 0 , 
will count from the end of the array!!!
meaning is: if queried and not find , 
will delete the last item!!

More Methods for Arrays

arr.includes(data);       //returns a boolean

arr.slice(start,end);
//end not included
//returns the items without deleting from the array

arr3 = arr.concat(arr1,arr2)
firstRemoved = arr.shift()
sortAsc = arr.sort();
reversed = arr.reverse();
changes the original array!!
toCSV = arr.toString()
JS Arrays - Filter,Map,Find,findIndex

arr.filter();


    arr.filter(function(array){
        return condition
    })


var words = ['spray', 'employee', 'limit', 
            'encyclopedia', 'elite', 'destruct'];

const result = words.filter(
    function(word) {
        return word.length > 5;
    }
);
console.log(result);
will return an array:

    ["employee", "encyclopedia", "destruct"]
The result will always be an array (even if no results returned)
The function can be extracted from the filter and be represented by a variable

    var words = ['spray', 'employee', 'limit', 
                'encyclopedia', 'elite', 'destruct'];
    var myLength = prompt();
    var filterType = function(word)
        {
            return word.length > myLength;
        };
    var result = words.filter(filterType);
To sreach all the array for all items with some letters inside

var words = ['Spray', 'employee', 'limit', 'encyclopedia', 'elite', 'destruct'];
function filterItems(query){
    return words.filter(
        function(e1) {
            return e1.toLowerCase().indexOf(query.toLowerCase()) > -1
        }
    )
}
console.log(filterItems(prompt()));

arr.find();

Returns only the first item answering the condition

var nums = [5, 12, 8, 130, 44];
var found = nums.find(
    function(element) {
        return element > 10;
    }
);
console.log(found);

Array.join()

makes a list of values from an array

arr.join(seperator);
Seperator defined as string, default is , (comma)

Arr.map(callBack)

transform the data in an array and create a new array

var nums = [5, 12, 8, 130, 44];
    var mapped = nums.map(
    function(x){
        return x * 2
    }
);
console.log(mapped);
Will Return

[10,24,16,260,44]

arr.Reduce

Returns the summ of all items is the array and create a math manipulation with StartNumber

var arr = [1,2,3,4];var reducer = function(acc, StartNumber){
    return acc+startNumber;
}
arr.reduce(reducer);
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