# [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.

### Using

```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.

### Using

```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.

### Using

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

console.log(numbers.every(isLimit));
//  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.

### Using

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

console.log(animal.includes('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.

### Using

```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.