Sådan manipuleres arrays i JavaScript

En vigtig del af ethvert programmeringssprog. De fleste gange er vi nødt til at udføre flere operationer på arrays, derfor denne artikel.

I denne artikel vil jeg vise dig forskellige metoder til at manipulere arrays i JavaScript [^^]

Hvad er arrays i JavaScript?

Inden vi fortsætter, skal du forstå, hvad arrays virkelig betyder.

I JavaScript er en matrix en variabel, der bruges til at gemme forskellige datatyper. Det gemmer grundlæggende forskellige elementer i en kasse og kan senere vurderes med variablen.

Erklæring om en matrix:

let myBox = []; // Initial Array declaration in JS

Arrays kan indeholde flere datatyper

let myBox = ['hello', 1, 2, 3, true, 'hi'];

Arrays kan manipuleres ved hjælp af flere handlinger kendt som metoder. Nogle af disse metoder giver os mulighed for at tilføje, fjerne, ændre og gøre meget mere til arrays.

Jeg vil vise dig et par i denne artikel, lad os rulle :)

NB: Jeg brugte pilefunktioner i dette indlæg. Hvis du ikke ved hvad dette betyder, skal du læse her. Pile-funktionen er en ES6-funktion .

toString ()

JavaScript-metoden toString()konverterer et array til en streng adskilt af et komma.

let colors = ['green', 'yellow', 'blue']; console.log(colors.toString()); // green,yellow,blue

tilslutte()

JavaScript- join()metoden kombinerer alle matrixelementer i en streng.

Det svarer til toString()metoden, men her kan du angive separatoren i stedet for standard kommaet.

let colors = ['green', 'yellow', 'blue']; console.log(colors.join('-')); // green-yellow-blue

konkat

Denne metode kombinerer to arrays sammen eller tilføjer flere elementer til en matrix og returnerer derefter en ny matrix.

let firstNumbers = [1, 2, 3]; let secondNumbers = [4, 5, 6]; let merged = firstNumbers.concat(secondNumbers); console.log(merged); // [1, 2, 3, 4, 5, 6]

skubbe()

Denne metode tilføjer elementer til slutningen af ​​en matrix og ændrer den oprindelige matrix.

let browsers = ['chrome', 'firefox', 'edge']; browsers.push('safari', 'opera mini'); console.log(browsers); // ["chrome", "firefox", "edge", "safari", "opera mini"]

pop ()

Denne metode fjerner det sidste element i et array og returnerer det.

let browsers = ['chrome', 'firefox', 'edge']; browsers.pop(); // "edge" console.log(browsers); // ["chrome", "firefox"]

flytte()

Denne metode fjerner det første element i et array og returnerer det.

let browsers = ['chrome', 'firefox', 'edge']; browsers.shift(); // "chrome" console.log(browsers); // ["firefox", "edge"]

skift ()

Denne metode tilføjer et element til begyndelsen af ​​et array og ændrer det originale array.

let browsers = ['chrome', 'firefox', 'edge']; browsers.unshift('safari'); console.log(browsers); // ["safari", "chrome", "firefox", "edge"]
Du kan også tilføje flere emner på én gang

splejsning ()

Dettemetode ændrer en matrix ved at tilføje, fjerne og indsætte elementer.

Syntaksen er:

array.splice(index[, deleteCount, element1, ..., elementN])
  • Indexher er udgangspunktet for at fjerne elementer i arrayet
  • deleteCounter antallet af elementer, der skal slettes fra dette indeks
  • element1, …, elementNer det eller de element (er), der skal tilføjes

Fjernelse af genstande

efter at have kørt splice () , returnerer det arrayet med elementet / elementerne fjernet og fjerner det fra det originale array.
let colors = ['green', 'yellow', 'blue', 'purple']; colors.splice(0, 3); console.log(colors); // ["purple"] // deletes ["green", "yellow", "blue"]
NB : deleteCount inkluderer ikke det sidste indeks i området.

Hvis den anden parameter ikke erklæres, fjernes hvert element, der starter fra det givne indeks, fra arrayet:

let colors = ['green', 'yellow', 'blue', 'purple']; colors.splice(3); console.log(colors); // ["green", "yellow", "blue"] // deletes ['purple']

I det næste eksempel fjerner vi 3 elementer fra arrayet og erstatter dem med flere elementer:

let schedule = ['I', 'have', 'a', 'meeting', 'tommorrow']; // removes 4 first elements and replace them with another schedule.splice(0, 4, 'we', 'are', 'going', 'to', 'swim'); console.log(schedule); // ["we", "are", "going", "to", "swim", "tommorrow"]

Tilføjer emner

For at tilføje emner skal vi indstille deleteCountnul

let schedule = ['I', 'have', 'a', 'meeting', 'with']; // adds 3 new elements to the array schedule.splice(5, 0, 'some', 'clients', 'tommorrow'); console.log(schedule); // ["I", "have", "a", "meeting", "with", "some", "clients", "tommorrow"]

skive()

Denne metode ligner, splice()men meget forskellig. Det returnerer underarrays i stedet for understrenge.

Denne metode kopierer en given del af et array og returnerer den kopierede del som et nyt array. Det ændrer ikke det oprindelige array.

Syntaksen er:

array.slice(start, end)

Her er et grundlæggende eksempel:

let numbers = [1, 2, 3, 4] numbers.slice(0, 3) // returns [1, 2, 3] console.log(numbers) // returns the original array

Den bedste måde at bruge slice()er at tildele den til en ny variabel.

let message = 'congratulations' const abbrv = message.slice(0, 7) + 's!'; console.log(abbrv) // returns "congrats!"

dele()

Denne metode bruges til strenge . Den deler en streng i understrenge og returnerer dem som en matrix.

Here’s the syntax:string.split(separator, limit);

  • The separator here defines how to split a string either by a comma.
  • The limit determines the number of splits to be carried out
let firstName = 'Bolaji'; // return the string as an array firstName.split() // ["Bolaji"]

another example:

let firstName = 'hello, my name is bolaji, I am a dev.'; firstName.split(',', 2); // ["hello", " my name is bolaji"]
NB: If we declare an empty array, like this  firstName.split(''); then each item in the string will be divided as substrings:
let firstName = 'Bolaji'; firstName.split('') // ["B", "o", "l", "a", "j", "i"]

indexOf()

This method looks for an item in an array and returns the index where it was found else it returns -1

let fruits = ['apple', 'orange', false, 3] fruits.indexOf('orange'); // returns 1 fruits.indexOf(3); // returns 3 friuts.indexOf(null); // returns -1 (not found)

lastIndexOf()

This method works the same way indexOf() does except that it works from right to left. It returns the last index where the item was found

let fruits = ['apple', 'orange', false, 3, 'apple'] fruits.lastIndexOf('apple'); // returns 4

filter()

This method creates a new array if the items of an array pass a certain condition.

The syntax is:

let results = array.filter(function(item, index, array) { // returns true if the item passes the filter });

Example:

Checks users from Nigeria

const countryCode = ['+234', '+144', '+233', '+234']; const nigerian = countryCode.filter( code => code === '+234'); console.log(nigerian); // ["+234", "+234"]

map()

This method creates a new array by manipulating the values in an array.

Example:

Displays usernames on a page. (Basic friend list display)

const userNames = ['tina', 'danny', 'mark', 'bolaji']; const display = userNames.map(item => { return '
  • ' + item + '
  • '; }) const render = '
      ' + display.join('') + '
    '; document.write(render);

    another example:

    // adds dollar sign to numbers const numbers = [10, 3, 4, 6]; const dollars = numbers.map( number => '$' + number); console.log(dollars); // ['$10', '$3', '$4', '$6'];

    reduce()

    This method is good for calculating totals.

    reduce() is used to calculate a single value based on an array.

    let value = array.reduce(function(previousValue, item, index, array) { // ... }, initial);

    example:

    To loop through an array and sum all numbers in the array up, we can use the for of loop.
    const numbers = [100, 300, 500, 70]; let sum = 0; for (let n of numbers) { sum += n; } console.log(sum);

    Here’s how to do same with reduce()

    const numbers = [100, 300, 500, 70]; const sum = numbers.reduce((accummulator, value) => accummulator + value , 0); console.log(sum); // 970
    If you omit the initial value, the total will by default start from the first item in the array.
    const numbers = [100, 300, 500, 70]; const sum = numbers.reduce((accummulator, value) => accummulator + value); console.log(sum); // still returns 970

    The snippet below shows how the reduce() method works with all four arguments.

    source: MDN Docs

    More insights into the reduce() method and various ways of using it can be found here and here.

    forEach()

    This method is good for iterating through an array.

    It applies a function on all items in an array

    const colors = ['green', 'yellow', 'blue']; colors.forEach((item, index) => console.log(index, item)); // returns the index and the every item in the array // 0 "green" // 1 "yellow" // 2 "blue"

    iteration can be done without passing the index argument

    const colors = ['green', 'yellow', 'blue']; colors.forEach((item) => console.log(item)); // returns every item in the array // "green" // "yellow" // "blue"

    every()

    This method checks if all items in an array pass the specified condition and returntrue if passed, else false.

    check if all numbers are positive
    const numbers = [1, -1, 2, 3]; let allPositive = numbers.every((value) => { return value >= 0; }) console.log(allPositive); // would return false

    some()

    This method checks if an item (one or more) in an array pass the specified condition and return true if passed, else false.

    checks if at least one number is positive
    const numbers = [1, -1, 2, 3]; let atLeastOnePositive = numbers.some((value) => { return value >= 0; }) console.log(atLeastOnePositive); // would return true

    includes()

    This method checks if an array contains a certain item. It is similar to .some(), but instead of looking for a specific condition to pass, it checks if the array contains a specific item.

    let users = ['paddy', 'zaddy', 'faddy', 'baddy']; users.includes('baddy'); // returns true

    If the item is not found, it returns false

    There are more array methods, this is just a few of them. Also, there are tons of other actions that can be performed on arrays, try checking MDN docs herefor deeper insights.

    Summary

    • toString() converts an array to a string separated by a comma.
    • join() combines all array elements into a string.
    • concat combines two arrays together or add more items to an array and then return a new array.
    • push() adds item(s) to the end of an array and changes the original array.
    • pop() removes the last item of an array and returns it
    • shift() removes the first item of an array and returns it
    • unshift() adds an item(s) to the beginning of an array and changes the original array.
    • splice() changes an array, by adding, removing and inserting elements.
    • slice() copiesa given part of an array and returns that copied part as a new array. It does not change the original array.
    • split() divides a string into substrings and returns them as an array.
    • indexOf() looks for an item in an array and returns the index where it was found else it returns -1
    • lastIndexOf() looks for an item from right to left and returns the last index where the item was found.
    • filter() creates a new array if the items of an array pass a certain condition.
    • map() creates a new array by manipulating the values in an array.
    • reduce() calculates a single value based on an array.
    • forEach() iterates through an array, it applies a function on all items in an array
    • every() checks if all items in an array pass the specified condition and return true if passed, else false.
    • some() checks if an item (one or more) in an array pass the specified condition and return true if passed, else false.
    • includes() checks if an array contains a certain item.

    Let’s wrap it here; Arrays are powerful and using methods to manipulate them creates the Algorithms real-world applications use.

    Let's do a create a small function, one that converts a post title into a urlSlug.

    URL slug is the exact address of a specific page or post on your site.

    When you write an article on Freecodecamp Newsor any other writing platform, your post title is automatically converted to a slug with white spaces removed, characters turned to lowercase and each word in the title separated by a hyphen.

    Here’s a basic function that does that using some of the methods we learnt just now.

    const url = '//bolajiayodeji.com/' const urlSlug = (postTitle) => { let postUrl = postTitle.toLowerCase().split(' '); let postSlug = `${url}` + postUrl.join('-'); return postSlug; } let postTitle = 'Introduction to Chrome Lighthouse' console.log(urlSlug(postTitle)); // //bolajiayodeji.com/introduction-to-chrome-lighthouse

    in postUrl, we convert the string to lowercase then we use the split()method to convert the string into substrings and returns it in an array

    ["introduction", "to", "chrome", "lighthouse"]

    in post slug we join the returned array with a hyphen and then concatenate it to the category string and main url.

    let postSlug = `${url}` + postUrl.join('-'); postUrl.join('-') // introduction-to-chrome-lighthouse

    Det er det, ret simpelt, ikke? :)

    Hvis du lige er kommet i gang med JavaScript, skal du tjekke dette lager her, jeg udarbejder en liste over grundlæggende JavaScript-uddrag, der spænder fra

    • Arrays
    • Kontrol flow
    • Funktioner
    • Objekter
    • Operatører

    Glem ikke at stjerne og dele! :)

    PS: Denne artikel blev først offentliggjort på min blog her