Difference between revisions of "JavaScript/C4/Array-methods-in-JS/English"
(Created page with "Title of the script: Array Methods Author: Jayesh Katta Ramalingaiah Domain Reviewer: Novice Reviewer: Keywords: JavaScript, HTML, callback, parameter, method, loop {...") |
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Learning Objectives | Learning Objectives | ||
|| In this tutorial, we will learn about: | || In this tutorial, we will learn about: | ||
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* Different '''Array Methods '''and | * Different '''Array Methods '''and | ||
* Advanced '''Array Loops '''in''' JS''' | * Advanced '''Array Loops '''in''' JS''' | ||
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|| Slide: System Specifications | || Slide: System Specifications | ||
|| This tutorial is recorded using: | || This tutorial is recorded using: | ||
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* '''Ubuntu Linux''' OS version 18.04 | * '''Ubuntu Linux''' OS version 18.04 | ||
* '''Visual Studio Code''' version 1.45.0 ('''code editor''') | * '''Visual Studio Code''' version 1.45.0 ('''code editor''') | ||
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|| Slide : Pre-requisites | || Slide : Pre-requisites | ||
|| To practice this tutorial, | || To practice this tutorial, | ||
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* You should be familiar with writing and executing''' JS''' files'''.''' | * You should be familiar with writing and executing''' JS''' files'''.''' | ||
* If not, please go through the prerequisite tutorials on this website. | * If not, please go through the prerequisite tutorials on this website. | ||
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* Pls download and extract the file. | * Pls download and extract the file. | ||
* Make a copy and then use them for practising. | * Make a copy and then use them for practising. | ||
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We’ll learn a few of them in this tutorial. | We’ll learn a few of them in this tutorial. | ||
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* '''length '''- '''Returns''' the length of the '''Array''' | * '''length '''- '''Returns''' the length of the '''Array''' | ||
* '''push '''- Adds a value at the end of the '''Array''' | * '''push '''- Adds a value at the end of the '''Array''' | ||
* '''pop '''- Removes a value from the end of the '''Array''' | * '''pop '''- Removes a value from the end of the '''Array''' | ||
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Press: Alt + L and Alt + O | Press: Alt + L and Alt + O | ||
− | || Save the file and | + | || Save the file and start the '''Live server'''. |
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Point to the browser '''Console''' tab | Point to the browser '''Console''' tab | ||
− | || In the web browser, open the '''Browser developer tools''' panel and go to the ''' | + | || In the '''web browser''', open the '''Browser developer tools''' panel and go to the '''Console tab'''. |
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'''<nowiki>Array(4) [ 1, 2, 3, 4 ]</nowiki>''' | '''<nowiki>Array(4) [ 1, 2, 3, 4 ]</nowiki>''' | ||
|| Observe here that the value '''4''' is added at the end of the '''array'''. | || Observe here that the value '''4''' is added at the end of the '''array'''. | ||
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|| Switch to Editor | || Switch to Editor | ||
|| Next, let’s use the '''pop method'''. | || Next, let’s use the '''pop method'''. | ||
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'''3''' | '''3''' | ||
− | || In the '''console''', we | + | || In the '''console''', we can see that the '''pop method''' has successfully removed the last '''element''' from the '''array'''. |
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* '''shift '''- Removes a value from the beginning of the '''Array''' | * '''shift '''- Removes a value from the beginning of the '''Array''' | ||
* '''unShift '''- Adds a value to the beginning of the '''Array''' | * '''unShift '''- Adds a value to the beginning of the '''Array''' | ||
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'''1''' | '''1''' | ||
|| Since the '''element''' is present in the '''array, index 1 '''is '''returned''' and printed in the '''log.''' | || Since the '''element''' is present in the '''array, index 1 '''is '''returned''' and printed in the '''log.''' | ||
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|| Switch to Editor | || Switch to Editor | ||
|| Next, let’s see the''' unshift method'''. | || Next, let’s see the''' unshift method'''. | ||
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'''<nowiki>Array(4) [ 0, 1, 2, 3 ]</nowiki>''' | '''<nowiki>Array(4) [ 0, 1, 2, 3 ]</nowiki>''' | ||
|| As you can see here, the value is added at the beginning of the '''array.''' | || As you can see here, the value is added at the beginning of the '''array.''' | ||
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|| Switch to Editor | || Switch to Editor | ||
|| Next, let’s see the '''shift method'''. | || Next, let’s see the '''shift method'''. | ||
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− | || Switch to ''' | + | || Switch to '''browser''' |
|| Switch back to the '''browser.''' | || Switch back to the '''browser.''' | ||
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* '''map '''- '''Loops''' over the '''Array '''and '''returns''' the '''modified Array''' | * '''map '''- '''Loops''' over the '''Array '''and '''returns''' the '''modified Array''' | ||
* '''filter '''- '''Loops''' over the '''Array '''with a '''condition''' and '''returns''' the '''filtered Array''' | * '''filter '''- '''Loops''' over the '''Array '''with a '''condition''' and '''returns''' the '''filtered Array''' | ||
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|| Only Narration | || Only Narration | ||
|| Let us look at an example for each of these '''methods''' and understand them better. | || Let us look at an example for each of these '''methods''' and understand them better. | ||
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|| Slide: Map Method | || Slide: Map Method | ||
|| '''map method '''is also very similar to '''forEach method.''' | || '''map method '''is also very similar to '''forEach method.''' | ||
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* It accepts a '''callback function''', | * It accepts a '''callback function''', | ||
* '''Loops''' over each and every value in the '''array''' | * '''Loops''' over each and every value in the '''array''' | ||
* Modifies it, and then '''returns''' the modified '''array''' | * Modifies it, and then '''returns''' the modified '''array''' | ||
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|| Switch to Editor | || Switch to Editor | ||
|| Next, let's learn about the '''filter method'''. | || Next, let's learn about the '''filter method'''. | ||
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|| In this tutorial, we have learnt: | || In this tutorial, we have learnt: | ||
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* Different''' Array Methods '''and | * Different''' Array Methods '''and | ||
* Advanced '''Array Loops '''in''' JS''' | * Advanced '''Array Loops '''in''' JS''' | ||
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|| Slide: Assignment | || Slide: Assignment | ||
|| As an assignment: | || As an assignment: | ||
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* Open the file '''assignment.js''' which you have created earlier. | * Open the file '''assignment.js''' which you have created earlier. | ||
* Clear the existing code. | * Clear the existing code. | ||
* '''Declare''' a '''variable marks''' | * '''Declare''' a '''variable marks''' | ||
* Assign an '''array '''to '''marks''' | * Assign an '''array '''to '''marks''' | ||
− | * '''The array''' should contain | + | * '''The array''' should contain 10 random numbers |
− | * Filter the '''marks array''' and display the '''marks '''divisible by | + | * Filter the '''marks array''' and display the '''marks '''divisible by 2 and 3 |
* Open the file '''MyPage.html''' in a web browser. | * Open the file '''MyPage.html''' in a web browser. | ||
* Observe the output in the '''browser’s console''' | * Observe the output in the '''browser’s console''' | ||
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* The video at the following link summarises the Spoken Tutorial project. | * The video at the following link summarises the Spoken Tutorial project. | ||
* Please download and watch it | * Please download and watch it | ||
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* We conduct workshops using spoken tutorials and give certificates. | * We conduct workshops using spoken tutorials and give certificates. | ||
* For more details, please write to us. | * For more details, please write to us. | ||
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Revision as of 14:22, 31 May 2021
Title of the script: Array Methods
Author: Jayesh Katta Ramalingaiah
Domain Reviewer:
Novice Reviewer:
Keywords: JavaScript, HTML, callback, parameter, method, loop
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Slide: Title | Hello and welcome to the spoken tutorial on “Array Methods in JS”. |
Slide:
Learning Objectives |
In this tutorial, we will learn about:
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Slide: System Specifications | This tutorial is recorded using:
However, you may use any other browser of your choice. |
Slide : Pre-requisites | To practice this tutorial,
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Slide: Code files |
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Slide: Array Methods | To make development work easy, we can use many of the inbuilt array methods of JS.
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Only Narration | Now, let us take an example for each of these methods and understand them better. |
Show VS editor | Open Visual Studio Code editor |
[Editor] Welcome Page -> Open Folder -> Practice-JS -> index.html & main.js
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Then open the files index.html and main.js as explained in the earlier tutorials.
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[Editor] Type:
<html lang="en"> <head> <title>Array Methods</title> </head> <body> <script src = "main.js" > </script> </body> </html> |
In the index.html file, replace the code as shown.
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Press: Ctrl + S
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Save the file and start the Live server. |
[Firefox] Press Ctrl + Shift + I
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In the web browser, open the Browser developer tools panel and go to the Console tab. |
Switch to Editor | Switch back to the editor. |
[Editor] Type:
console.log(arr.length); |
In the main.js file, replace the code as shown. |
[Editor] Highlight:
|
Here, I have created a variable named arr and assigned an array with elements 1, 2 and 3. |
[Editor] Highlight:
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And in the console, I am logging arr.length, which prints the length of the array. |
Press: Ctrl + S | Save the file. |
Switch to Browser | Switch back to the browser. |
[Browser] [Console Tab]:
Highlight: 3 |
Here we see 3.
That’s because there are 3 elements, and so the length of the array is 3.
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Switch to Editor | Switch back to the editor. |
[Editor] Type:
const arr = [1, 2, 3]; console.log(arr.push(4));
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In the main.js file, replace the code as shown. |
[Editor] Highlight:
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I’m using the push method to add an element to the end of the array
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[Editor] Highlight:
console.log(arr.push(4)); |
The push method returns the length of the array.
|
Press: Ctrl + S | Save the file. |
Switch to Browser | Switch back to the browser. |
[Browser] [Console Tab]:
Highlight: 4 |
In the console, we can see that the length of the array after pushing the value, is seen as 4. |
[Browser] [Console Tab]:
Highlight:
|
Observe here that the value 4 is added at the end of the array.
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Switch to Editor | Next, let’s use the pop method. |
[Editor] Type:
console.log(arr.pop()); console.log(arr); |
In the main.js file, replace the code as shown. |
[Editor] Highlight:
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Here, I used the pop method.
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[Editor] Highlight:
console.log(arr.pop()); |
The pop method returns the deleted value in the array.
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Press: Ctrl + S | Save the file. |
Switch to Browser | Switch back to the browser. |
[Browser] [Console Tab]:
Highlight: 3 |
In the console, we can see that the pop method has successfully removed the last element from the array.
|
Slide: Array Methods |
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Only Narration | Let us take an example for each of these methods and understand them better. |
Switch to Editor | Switch back to the editor. |
[Editor] Type:
console.log(arr.indexOf(2)); |
In the main.js file, replace the code as shown. |
[Editor] Highlight:
|
Here, I’m using the indexOf method and passing the value 2 to it.
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Press: Ctrl + S | Save the file. |
Switch to Browser | Switch back to the browser. |
[Browser] [Console Tab]:
Highlight: 1 |
Since the element is present in the array, index 1 is returned and printed in the log.
|
Switch to Editor | Next, let’s see the unshift method. |
[Editor] Type:
arr.unshift(0); console.log(arr); |
In the main.js file, replace the code as shown. |
[Editor] Highlight:
|
Here, I’m using the unshift method and passing the value 0 to it.
|
Press: Ctrl + S | Save the file. |
Switch to Browser | Switch back to the browser. |
[Browser] [Console Tab]:
Highlight: Array(4) [ 0, 1, 2, 3 ] |
As you can see here, the value is added at the beginning of the array. |
Switch to Editor | Next, let’s see the shift method. |
[Editor] Type:
arr.shift(); console.log(arr); |
In the main.js file, replace the code as shown. |
[Editor] Highlight:
|
Here, I’m using the shift method, which deletes one value from the beginning of the array. |
Press: Ctrl + S | Save the file. |
Switch to browser | Switch back to the browser. |
[Browser] [Console Tab]:
Highlight:
|
Notice here that 1 is removed from the array.
|
Slide: Array Methods |
|
Only Narration | Let us look at an example for each of these methods and understand them better. |
[Editor] Type:
arr.forEach((item) => console.log(item)); |
In the main.js file, replace the code as shown. |
[Editor] Highlight:
|
Here, I’m using a forEach method to loop over the array.
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[Editor] Highlight:
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Here, I will pass any variable name as a parameter.
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[Editor] Highlight:
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On every iteration, I log the value. |
Press: Ctrl + S | Save the file. |
Switch to Browser | Switch back to the browser. |
[Browser] [Console Tab]:
Highlight:
2 3 |
Look here. The array has looped over.
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Switch to Editor | Next, let’s learn about the map method.
|
[Editor] Type:
const modifiedArr = arr.map((item) => item * 2); console.log(modifiedArr); |
In the main.js file, replace the code as shown. |
[Editor] Highlight:
|
Here, I’m using the map method.
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Slide: Map Method | map method is also very similar to forEach method.
|
[Editor] Highlight:
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’m storing the modified array in the variable modifiedArr. |
[Editor] Highlight:
console.log(modifiedArr); |
In the console, I’m logging the modifiedArr variable for verification. |
Press: Ctrl + S | Save the file. |
Switch to Browser | Switch back to the browser. |
[Browser] [Console Tab]:
Highlight:
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Observe the console.
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Switch to Editor | Next, let's learn about the filter method. |
[Editor] Type:
const filteredArr = arr.filter((item) => item < 3); console.log(filteredArr); |
In the main.js file, replace the code as shown. |
[Editor] Highlight:
|
Here, I’m using the filter method.
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[Editor] Highlight:
item < 3 |
Here, inside the callback function, I have mentioned a condition.
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const filteredArr = | The returned values are stored in the variable filteredArr. |
[Editor] Highlight:
|
Here, I’m logging the filteredArr variable for verification. |
Press: Ctrl + S | Save the file. |
Switch to Browser | Switch back to the browser. |
[Browser] [Console Tab]:
Highlight:
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In the console, we have the filtered array.
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Only Narration | With this, we have come to the end of this tutorial.
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Slide: Summary
|
In this tutorial, we have learnt:
|
Slide:
[Highlight]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array |
We have covered only a few array methods in this tutorial.
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Slide: Assignment | As an assignment:
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Slide: About Spoken Tutorial Project |
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Slide: Spoken tutorial workshops |
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Slide: Forum questions | Pls post your timed queries in this forum |
Slide: Acknowledgement | Spoken Tutorial Project is funded by the Ministry of Education (MoE), Government of India |
Slide: Thanks | The script for this tutorial is contributed by Jayesh and this is Praveen signing off. Thank you for joining |