כיצד לנהל מערכים ב- JavaScript

תִכנוּת

חלק חשוב בכל שפת תכנות. לרוב עלינו לבצע מספר פעולות על מערכים, ומכאן מאמר זה.

במאמר זה הייתי מראה לך שיטות שונות לתפעל מערכים ב- JavaScript [^^]

מהם מערכים ב- JavaScript?

לפני שנמשיך, עליך להבין מה המשמעות של מערכים באמת.

ב- JavaScript, מערך הוא משתנה המשמש לאחסון סוגי נתונים שונים. זה בעצם מאחסן אלמנטים שונים בתיבה אחת וניתן להעריך אותו אחר כך באמצעות המשתנה.

הכרזת מערך:

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

מערכים יכולים להכיל מספר סוגי נתונים

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

ניתן לתפעל מערכים באמצעות מספר פעולות המכונות שיטות. חלק משיטות אלה מאפשרות לנו להוסיף, להסיר, לשנות ולעשות הרבה יותר למערכים.

הייתי מראה לכם כמה במאמר זה, בואו נתגלגל :)

הערה: השתמשתי בפונקציות חץ בהודעה זו, אם אינך יודע מה פירוש הדבר, עליך לקרוא כאן. פונקציית החץ היא תכונה של ES6 .

toString ()

שיטת JavaScript toString()ממירה מערך למחרוזת המופרדת בפסיק.

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

לְהִצְטַרֵף()

join()שיטת JavaScript משלבת את כל רכיבי המערך למחרוזת.

זה דומה toString()לשיטה, אך כאן תוכלו לציין את המפריד במקום את פסיק ברירת המחדל.

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

concat

שיטה זו משלבת שני מערכים יחד או מוסיפה פריטים נוספים למערך ואז מחזירה מערך חדש.

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

לִדחוֹף()

שיטה זו מוסיפה פריטים בסוף מערך ומשנה את המערך המקורי.

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

פּוֹפּ()

שיטה זו מסירה את הפריט האחרון במערך ומחזירה אותו.

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

מִשׁמֶרֶת()

שיטה זו מסירה את הפריט הראשון במערך ומחזירה אותו.

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

ביטול משמרת ()

שיטה זו מוסיפה פריט (ים) לתחילת מערך ומשנה את המערך המקורי.

let browsers = ['chrome', 'firefox', 'edge']; browsers.unshift('safari'); console.log(browsers); // ["safari", "chrome", "firefox", "edge"]
ניתן להוסיף מספר פריטים בו זמנית

אִחוּי()

זֶההשיטה משנה מערך, על ידי הוספה, הסרה והוספה של אלמנטים.

התחביר הוא:

array.splice(index[, deleteCount, element1, ..., elementN])
  • Indexהנה נקודת המוצא להסרת אלמנטים במערך
  • deleteCountהוא מספר האלמנטים שיימחקו מאותו אינדקס
  • element1, …, elementNהוא האלמנט (ים) שיש להוסיף

הסרת פריטים

לאחר הפעלת splice () , הוא מחזיר את המערך כשהפריט (ים) הוסרו ומסיר אותו מהמערך המקורי. 
let colors = ['green', 'yellow', 'blue', 'purple']; colors.splice(0, 3); console.log(colors); // ["purple"] // deletes ["green", "yellow", "blue"]
הערה : deleteCount אינו כולל את האינדקס האחרון בטווח.

If the second parameter is not declared, every element starting from the given index will be removed from the array:

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

In the next example we will remove 3 elements from the array and replace them with more items:

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"]

Adding items

To add items, we need to set the deleteCount to zero

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"]

slice()

This method is similar to splice() but very different. It returns subarrays instead of substrings.

This method copies a given part of an array and returns that copied part as a new array. It does not change the original array.

The syntax is:

array.slice(start, end)

Here’s a basic example:

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

The best way to use slice() is to assign it to a new variable.

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

split()

This method is used for strings. It divides a string into substrings and returns them as an array.

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

    That’s it, pretty simple, right? :)

    If you’re just getting started with JavaScript, you should check this repository here, I’m compiling a list of basic JavaScript snippets ranging from

    • Arrays
    • Control flow
    • Functions
    • Objects
    • Operators

    Don’t forget to Star and share! :)

    PS: This article was first published on my blog here