array object in javascript

1//Creating a list
2var fruits = ["Apple", "Banana", "Cherry"];
3
4//Creating an empty list
5var books = [];
6
7//Getting element of list
8//Lists are ordered using indexes
9//The first element in an list has an index of 0, 
10//the second an index of 1,
11//the third an index of 2,
12//and so on.
13console.log(fruits[0]) //This prints the first element 
14//in the list fruits, which in this case is "Apple"
15
16//Adding to lists
17fruits.push("Orange") //This will add orange to the end of the list "fruits"
18fruits[1]="Blueberry" //The second element will be changed to Blueberry
19
20//Removing from lists
21fruits.splice(0, 1) //This will remove the first element,
22//in this case Apple, from the list
23fruits.splice(0, 2) //Will remove first and second element
24//Splice goes from index of first argument to index of second argument (excluding second argument)

1//create an array like so:
2var colors = ["red","blue","green"];
3
4//you can loop through an array like this:
5for (var i = 0; i < colors.length; i++) {
6    console.log(colors[i]);
7}

1var names = ["Sanjith", "Pranav", "Aadya", "Saharsh"]

1var widgetTemplats = [
2    {
3        name: 'compass',
4        LocX: 35,
5        LocY: 312
6    },
7    {
8        name: 'another',
9        LocX: 52,
10        LocY: 32
11    }
12]

1
2const person = {firstName:"John", lastName:"Doe", age:46};
3 

1
2Some use cases of looping through an array in the functional programming way in JavaScript:
3)=============================================================
41. Just loop through an array
5
6const myArray = [{x:100}, {x:200}, {x:300}];
7
8myArray.forEach((element, index, array) => {
9    console.log(element.x); // 100, 200, 300
10    console.log(index); // 0, 1, 2
11    console.log(array); // same myArray object 3 times
12});
13Note: Array.prototype.forEach() is not a functional way strictly speaking, as the function it takes as the input parameter is not supposed to return a value, which thus cannot be regarded as a pure function.
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152. Check if any of the elements in an array pass a test
16
17
18const people = [
19    {name: 'John', age: 23}, 
20    {name: 'Andrew', age: 3}, 
21    {name: 'Peter', age: 8}, 
22    {name: 'Hanna', age: 14}, 
23    {name: 'Adam', age: 37}];
24
25const anyAdult = people.some(person => person.age >= 18);
26console.log(anyAdult); // true
27
28
29)=============================================================
303. Transform to a new array
31const myArray = [{x:100}, {x:200}, {x:300}];
32
33const newArray= myArray.map(element => element.x);
34console.log(newArray); // [100, 200, 300]
35Note: The map() method creates a new array with the results of calling a provided function on every element in the calling array.
36)=============================================================
374. Sum up a particular property, and calculate its average
38const myArray = [{x:100}, {x:200}, {x:300}];
39
40const sum = myArray.map(element => element.x).reduce((a, b) => a + b, 0);
41console.log(sum); // 600 = 0 + 100 + 200 + 300
42
43const average = sum / myArray.length;
44console.log(average); // 200
45
46)=============================================================
475. Create a new array based on the original but without modifying it
48const myArray = [{x:100}, {x:200}, {x:300}];
49
50const newArray= myArray.map(element => {
51    return {
52        ...element,
53        x: element.x * 2
54    };
55});
56
57console.log(myArray); // [100, 200, 300]
58console.log(newArray); // [200, 400, 600]
59
60)=============================================================
616. Count the number of each category
62const people = [
63    {name: 'John', group: 'A'}, 
64    {name: 'Andrew', group: 'C'}, 
65    {name: 'Peter', group: 'A'}, 
66    {name: 'James', group: 'B'}, 
67    {name: 'Hanna', group: 'A'}, 
68    {name: 'Adam', group: 'B'}];
69
70const groupInfo = people.reduce((groups, person) => {
71    const {A = 0, B = 0, C = 0} = groups;
72    if (person.group === 'A') {
73        return {...groups, A: A + 1};
74    } else if (person.group === 'B') {
75        return {...groups, B: B + 1};
76    } else {
77        return {...groups, C: C + 1};
78    }
79}, {});
80
81console.log(groupInfo); // {A: 3, C: 1, B: 2}
82
83)=============================================================
847. Retrieve a subset of an array based on particular criteria
85const myArray = [{x:100}, {x:200}, {x:300}];
86
87const newArray = myArray.filter(element => element.x > 250);
88console.log(newArray); // [{x:300}] 
89Note: The filter() method creates a new array with all elements that pass the test implemented by the provided function.
90
918. Sort an array
92const people = [
93  { name: "John", age: 21 },
94  { name: "Peter", age: 31 },
95  { name: "Andrew", age: 29 },
96  { name: "Thomas", age: 25 }
97];
98
99let sortByAge = people.sort(function (p1, p2) {
100  return p1.age - p2.age;
101});
102
103console.log(sortByAge);
104enter image description here
105)=============================================================
1069. Find an element in an array
107const people = [ {name: "john", age:23},
108                {name: "john", age:43},
109                {name: "jim", age:101},
110                {name: "bob", age:67} ];
111
112const john = people.find(person => person.name === 'john');
113console.log(john);
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