[JavaScript]How to examine specific elements of an array

I had a chance to teach about arrays in PHP, so how was Javascript?I thought, I tried to summarize.

Retrieve only a specific element of an array

Use array.filter. Returns an array by filtering only the elements that meet the specified criteria.


let animal= ['pig', 'cow', 'pig', 'lion', 'cat']; 

let animalPig = animal.filter(function(n){
    return n === 'pig'
// If you write in the Arrow function
let animalPig = animal.filter(n => n === 'pig');

// ['pig', 'pig']


For object

let animal= [
    { name: 'pig', num: '2'},
    { name: 'cow', num: '4'},
    { name: 'pig', num: '3'},
    { name: 'lion', num: '2'},
    { name: 'cat', num: '1'},
let animalNumTwo =  matches.filter(n => n.num === '2');

// outputed object
// [
//     { name: 'pig', num: '2'},
//     { name: 'lion', num: '2'},
// ];


It can also be used to count the number of specific elements in an array in an application.

// Count how many pigs there are
let animal= ['pig', 'cow', 'pig', 'lion', 'cat'];
let count = animal.filter(n => n === 'pig').length;

// count === 2


Find a specific element in an array

array.find Returns the value of the first element in the array that satisfies the condition.


let numbers = [7, 120, 40, 33, 150];
let number = numbers.find(n => n > 100);

// number === 120


Determines whether all elements in the array meet the condition

Use array.every.If all elements meet the condition, it is true, and if not satisfied, it returns false.
Note: every returns true for an empty array.


var isLimit = (n) => n < 10;
let numbers = [1, 8, 9, 5];

//  true


For example, check whether the date is set, etc.

let isDateTime = eventList.every(value => value.datetime);

//true if eventList element datetime has a value


Determine whether an array contains a specific element

Use array.includes.Returns true if a particular element is contained in an array, false if it is not.


let animal= ['pig', 'cow', 'pig', 'lion', 'cat']; 

// true


Find out if there are any elements in the array that meet the conditions

Use array.some.Returns true when any one element of the array satisfies the condition.
Note: some returns false for empty arrays.


let numbers = [1, 8, 9, 5];
let isEven = (n) => n % 2 === 0;

// true because there are 8


The difference between includes and some?

Includes simply determines whether a particular element is included.
Some can determine whether certain conditions (functions can be used) are met.
If you want to find a simple array, includes is simple.
If you want to find a specific value from an associative array or object, you may want to use some and use a function.