Scratch (programming language)

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Scratch
Scratch logo
ParadigmEvent-driven, visual, block-based programming language
First appeared2002 (2002) (first prototype)
2005 (2005) (second prototype)
January 8, 2007; 12 years ago (2007-01-08) (public launch)
May 9, 2013; 6 years ago (2013-05-09) (Scratch 2.0)
January 2, 2019; 8 months ago (2019-01-02) (Scratch 3.0)
Implementation languageSqueak (Scratch 0.x, 1.x)
ActionScript (Scratch 2.0)
JavaScript (Scratch 3.0)
OSWindows, macOS, Linux (runs on most browsers)
LicenseGPLv2 and Scratch Source Code License
Filename extensions.scratch (Scratch 0.x)
.sb, .sprite (Scratch 1.x)
.sb2, .sprite2 (Scratch 2.0)
.sb3, .sprite3 (Scratch 3.0)
Websitescratch.mit.edu
Dialects
Commodore Google[citation needed]
Influenced by
Logo, Smalltalk, HyperCard, StarLogo, AgentSheets, AgentCubes, Etoys
Influenced
ScratchJr, Snap!

Scratch is a block-based visual programming language and online community targeted primarily at children. Users of the site can create online projects using a block-like interface. The service is developed by the MIT Media Lab, has been translated into 70+ languages, and is used in most parts of the world.[1] Scratch is taught and used in after-school centers, schools, and colleges, as well as other public knowledge institutions. As of May 2019, community statistics on the language's official website show more than 40 million projects shared by over 40 million users, and almost 40 million monthly website visits.[1]

"Scratch Cat", the mascot of the website

Scratch takes its name from a technique used by disk jockeys called "scratching", where vinyl records are clipped together and manipulated on a turntable to produce different sound effects and music. Like scratching, the website lets users mix together different media (including graphics, sound, and other programs) in creative ways by "remixing" projects.[2][3]

Philosophy[edit]

Scratch encourages the sharing, reuse, and combination of code, as indicated by their slogan, "Imagine, Program, Share".[4] Users can make their own projects, or they may choose to "remix" someone else's project. Projects created and remixed with Scratch are licensed under the Creative Commons Attribution-Share Alike License.[5] Scratch automatically gives credit to the user who created the original project and program.[2]

It is part of research to design new technologies to enhance learning in after-school centers and other informal education settings, and broaden opportunities for youth who can possibly become designers and inventors. Scratch was developed based on ongoing interaction with youth and staff at Computer Clubhouses. The use of Scratch at Computer Clubhouses served as a model for other after-school centers demonstrating how informal learning settings can support the development of technological fluency.[6]

History[edit]

The MIT Media Lab's Lifelong Kindergarten group, led by Mitchel Resnick, in partnership with the Montreal-based consulting firm, the Playful Invention Company, co-founded by Brian Silverman and Paula Bonta, together developed the first desktop-only version of Scratch in 2003. It started as a basic coding language, with no labeled categories and no green flag.[7] Scratch was made with the intention to teach kids to code.[7]

The 2.0 Scratch homepage skin

On May 6, 2013, Scratch closed for three days to update to Scratch 2.0 and was released on May 9, 2013.[8] The update changed the look of the site and included an online project editor. An offline Scratch 2 Editor is also available.[9] With its introduction, custom blocks could be defined within projects, along with several other improvements.[10]

In 2017, Scratch 2.0 became available online and as an application for Windows, macOS, Linux (Adobe Air required), and unofficially for Android as an APK file. The Scratch 2.0 Offline editor could be downloaded for Windows, Mac and Linux directly from Scratch's website but later on the support for Linux was dropped. The unofficial mobile version must be downloaded from the Scratch forums.[11][12]

Scratch 3.0[edit]

The Scratch 3.0 interface includes many new features.
The Scratch 3.0 interface

Scratch 3.0 was first announced by the Scratch Team in 2016. Several public alpha versions were released between then and January 2018, after which the pre-beta "Preview" versions were released.[13] A beta version of Scratch 3.0 was released on the 1st August 2018, replacing the pre-beta "preview"[14] and is available for use on most browsers, with the notable exception of Internet Explorer.[15] The first release version of Scratch 3.x, 3.0, was released on January 2nd, 2019.

The most notable difference between 3.x and the iterations before it is a "material" design that spans across the entire interface. The "project player" part of the website was also updated to this design at the release of Scratch 3.0, as the website has been slowly updated since 2016 to material design.

Scratch 3.x is not based on 2.0 - rather, it is a completely new JavaScript-based code-base made up of multiple components such as "Scratch-GUI", the main part of the program, "Scratch-VM", which interprets code, and "Scratch-Render", the rendering engine.

In 3.x, the stage's presence is also put back onto the right-hand side of the screen like in 1.x.x versions, rather than the left as seen in 2.0.x versions. Other features include language translation, text-to-speech, and compatibility with several physical pieces of technology such as the BBC micro-bit;[15] these features are available via built-in plug-ins known as "extensions". Users can also create their own extensions for Scratch 3.0 using JavaScript, similar to how users could also create extensions using JavaScript for a special version of Scratch 2.0 called "Scratch X" (which itself is no longer supported due to the release of 3.0). Other extensions that were added include Makey Makey, Text to Speech, LEGO MINDSTORMS EV3, LEGO Education WeDo 2.0, and BB3. Additionally, some features of Scratch 2.0 were moved to extensions, including music, video sensing, and pen.

Unlike Scratch 2.0, Scratch 3.0 follows semantic versioning, therefore the "minor" number of the version number changes, rather than only the "patch" number changing.[citation needed] However, currently, there is no part in the Scratch 3 code that actually holds a version number, and there is currently not an "About" dialog to report the version number yet.

Scratch 3.0 was officially released by MIT on January 2nd, 2019.

.sb file[edit]

An .sb file is the file format used to store projects created in the Scratch programming language editor up to version 1.4.[16] sb is no longer used in the current version of Scratch and was replaced by the .sb2 file in Scratch 2.0.

File Structure[edit]

The .sb file is divided into four sections.

header[edit]

The 10-byte header contains the ASCII string 'ScratchV02' in versions higher than 1.2, and contains the string 'ScratchV01' in versions 1.2 and below.

infoSize[edit]

Encodes the length of the project's infoObjects. A four-byte long, 32-bit, big-Endian integer.

infoObjects[edit]

A dictionary-format data section. It contains the following keys:

  • thumbnail: a thumbnail of the project's stage
  • author: the username of the project's creator
  • comment: the Project Notes
  • history: save and upload log
  • scratch-version: the version of Scratch used to save the file

contents[edit]

An object table with the Stage as the root. All objects in the program are stored here as references.

.sb2 file[edit]

The .sb2 file format is used by the programming language Scratch (as of Oct 2015) when exporting a project. In the previous version of Scratch (version 1.4) the project was exported as an .sb file but was changed in the update to version 2.0. This has now been changed to .sb3 as of January 2019, in the release of Scratch 3.0.

.sb2 files are zip files containing a .json file as well as the contents of the Scratch project including sounds (stored as .wav) and images (stored as .png). Each filetype, excluding the project.json, is stored as a number, starting at 0 and counting up with each additional file. The image file labelled '0.png' is always a 480x360 white image, but '0.wav' will still be the earliest non-deleted file.

.sbx files are for the ScratchX experimental version of Scratch. See https://github.com/llk/scratchx/wiki for more. The ScratchX site indicates that Scratch 2.0 .sb2 extensions were to have been discontinued in November 2015.

Educational use[edit]

Scratch was popular in the United Kingdom through Code Clubs. Scratch is used as the introductory language because the creation of interesting programs is relatively easy, and skills learned can be applied to other programming languages such as Python and Java.

Comparison of Scratch 1.4 and Scratch 2

Scratch is not exclusively for creating games. With the provided visuals, programmers can create animations, text, stories, music, and more. There are already many programs which students can use to learn topics in math, history, and even photography. Scratch allows teachers to create conceptual and visual lessons and science lab assignments with animations that help visualize difficult concepts. Within the social sciences, instructors can create quizzes, games, and tutorials with interactive elements. Using Scratch allows young people to understand the logic of programming and how to creatively build and collaborate.[17]

Scratch is taught to more than 800 schools and 70 colleges of DAV organization in India and across the world.[18][19]

Harvard University lecturer Dr. David J. Malan prefers using Scratch over commonly used introductory programming languages, such as Java or C, in his introductory computer science course. However, there is a limited benefit in a college level education. Malan switched his course's language to C after the first week.[20][21]

Criticism[edit]

There has been a substantial amount of criticism[by whom?] of Scratch as an introductory programming language due to its drag-and-drop style potentially giving children (its target audience) the wrong idea of programming and being too "sugar-coated" or watered-down as compared to other programming languages such as C++, C, Java, or JavaScript.

There have been criticisms of Scratch 2 that it was based on Adobe technology, with some assuming it was based on Adobe Flash which is obsolete from April 9, 2019[22]. Scratch 2's primary dependency is on Adobe AIR, which remains available although only for client operations on Microsoft Windows and Apple Macs.

Scratch 2's web-based programming platform can be slow on low-power computers.[23]

However, Scratch 3.0 uses JavaScript including WebGL, a more updated platform that also works on mobile devices.

When the first version of Scratch 3 was released, it received a mixed reaction from the community. Although some resistance was attributed to change in general, complaints have been made that the redesign looks unprofessional and childish.[24] 3.x has also been panned for having poor backwards compatibility with projects made using older versions of Scratch, including bugs and projects that don't load.[25][26]

User interface[edit]

The Scratch interface has three main sections: a stage area, blocks palette, and a coding area to place and arrange the blocks into runnable scripts.

The stage area features the results (i.e., animations, turtle graphics, etc., either in a small or normal size, with a full-screen also available) and all sprites thumbnails listed in the bottom area. The stage uses x and y coordinates, with 0,0 being the stage center; the stage is 480 pixels wide, and 360 pixels tall, x:240 being the far right, x:-240 being the far left, y:180 being the top, and y:-180 being the bottom.[8] With a sprite selected at the bottom of the staging area, blocks of commands can be applied to it by dragging them from the blocks palette into the coding area, containing all the scripts associated with the selected sprite. Each can also be individually tested under different conditions and parameters via a double-click. Under the Scripts tab, all available blocks are listed and categorized. There is also an extensions tab which allows other blocks to be added.

Next, to the Scripts tab, there is the Costumes tab, where users can change the look of the sprite in order to create various effects, including animation.[8] The last tab is the Sounds tab, where users insert sounds and music to a sprite.[27]

When creating sprites and backgrounds, users can draw their own sprite manually with "Paint Editor" provided by Scratch,[8] choose a Sprite from a library, or uploading a picture.[27]

3.x[edit]

The Scratch 3.0 development environment on startup.

The user interface for Scratch 3.x is designed with a flat look, with the blocks palette on the left, the scripts area in the middle, and the stage on the right. The blocks palette is designed as one scrollable interface, with labeled sections that bring the user to different sections of it. At the bottom left are the extensions; when clicked, it brings up a list of the Scratch extensions that can be added to the blocks palette as new sections. Bigger blocks in the coding area are designed to work on touch devices.

The table below shows the categories of the block palette in Scratch 3.x (some categories previously seen in 2.0 are now extensions and are therefore not listed):

Category Notes    Category Notes
  Motion Moves sprites, changes angles and changes X and Y values.      Sensing Sprites can interact with the surroundings the user has created
  Looks Controls the visuals of the sprite; attach speech or thought bubble, change of background, enlarge or shrink, transparency, shade   Operators Mathematical operators, random number generator, and-or statement that compares sprite positions
  Sound Plays audio files and effects. Programmable sequences are now available as an extension category named "Music".   Variables Variable and List usage and assignment
  Events Contains event handlers placed on the top of each group of blocks   My Blocks Custom procedures (blocks).
  Control Conditional if-else statement, "forever", "repeat", and "stop", etc

It also provides 'extensions':

2.0[edit]

Scratch 2.0 development environment and its different areas at startup
Hello, World! in Scratch 2.0

In Scratch 2.0, the stage area is on the left side, with the blocks palette in the middle. Contrary to 3.0, the blocks palette is made of discrete sections that are not scrollable from one to the next. On the right side is the coding area. In 2.0, extensions are filed inside of the "more blocks" section of the blocks palette

In comparison to the previous versions of Scratch, the areas have been rearranged in version 2.0, as previously the blocks palette was in the left area, the selected sprite area and scripts area associated with a selected sprite were in the middle of the screen, and the stage area with sprites thumbnails listed below it were in the right area of the screen.[28]

The table below shows the different sections of the blocks palette in Scratch 2.0:

Category Notes    Category Notes
  Motion Moves sprites, changes angles and changes X and Y values.      Events Contains event handlers placed on the top of each group of blocks
  Looks Controls the visuals of the sprite; attach speech or thought bubble, change of background, enlarge or shrink, transparency, shade   Control Conditional if-else statement, "forever", "repeat", and "stop", etc
  Sound Plays audio files and programmable sequences   Sensing Sprites can interact with the surroundings the user has created
  Pen Draw on the canvas by controlling pen width, color, and shade. Allows for turtle graphics.   Operators Mathematical operators, random number generator, and-or statement that compares sprite positions
  Data Variable and List usage and assignment   More Blocks Custom procedures (blocks) and external devices control and can import from PicoBoard or Lego WeDo 1.0/2.0

Extensions[edit]

Scratch 2 and 3 both support extensions, which add extra blocks and features that can be used in projects. In Scratch 2, the extensions were all hardware based, but software based extensions were added in Scratch 3. In addition to adding new extensions, Scratch 3.x also moved some default blocks in Scratch 2.0 into the extensions section, such as Music and Pen. As of Scratch 3.x, the Scratch team plans to regularly add new extensions.

Physical[edit]

  • EV3 - control motors and receive sensor data from the LEGO EV3
  • Makey Makey - use the Makey Makey to control your projects
  • LEGO Education WeDo 2.0 - control motors and receive sensor data from the LEGO WeDo
  • BBC micro:bit - use of a BBC micro:bit to control projects

Digital[edit]

Many of the digital extensions in Scratch 3 used to be regular block categories that were moved to the extensions section to reduce clutter. These include:

  • Music - Play digital instruments (drums, trumpets, violins, pianos and more)
  • Pen - Draw on the Stage with a variety of thicknesses and color
  • Video Sensing - Detect motion with the camera.

However, new digital extensions have been added that were not available in Scratch 2 in collaborations with companies. These include:

  • Text to Speech - Converts words in a text into voice output (variety of voices, supplied by Amazon)
  • Translate - Uses Google Translate to translate text from one language into a variety of other languages

Community of users[edit]

The Scratch website after the release of public project sharing in late 2007

Scratch is used in many different settings: schools,[29] museums,[30] libraries,[2] community centers, and homes. Although Scratch's main user age group is 8–18 years of age, Scratch has also been created for educators and parents. This wide outreach has created many surrounding communities, both physical and digital.[1]

Online community[edit]

On Scratch, members have the capability to share their projects and get feedback. Projects can be uploaded directly from the development environment to the Scratch website and any member of the community can download the full source code to study or to remix into new projects.[31][32] Members can also create project studios, comment, tag, favorite, and "love" others' projects, follow other members to see their projects and activity, and share ideas. Projects range from games to animations to practical tools. Additionally, to encourage creation and sharing amongst users, the website frequently establishes "Scratch Design Studio" challenges.[33]

The MIT Scratch Team ensures that this community maintains a friendly and respectful environment for people of all ages, races, ethnicities, religions, sexual orientations, and gender identities. All members are asked to provide feedback constructively and report any content that does not follow the community guidelines. To further ensure this community, the Scratch Team manages site activity and responds to reports on a daily basis.[34][35]

There is also an online community for educators called ScratchEd. ScratchEd was developed and supported by the Harvard Graduate School of Education. In this community, Scratch educators share stories, exchange resources, ask questions, and find people.[36]

Scratch Wiki[edit]

The Scratch Wiki is a medium-sized wiki for the Scratch educational programming language and its website, history, and phenomena surrounding it. The wiki is supported by the Scratch Team (developers of Scratch), but is primarily written by Scratchers (users of Scratch) for information regarding projects and things that interest users,[37] though editors must go through an account request process to avoid vandalism.

Events[edit]

Scratch Educators can gather in person at Scratch Educator Meetups. At these gatherings, Scratch Educators learn from each other and share ideas and strategies that support computational creativity.[38]

An annual "Scratch Day" is declared in May each year. Community members are encouraged to host an event on or around this day, large or small, that celebrates Scratch. These events are held worldwide, and a listing can be found on the Scratch Day website.[39]

Features and derivatives[edit]

Scratch uses event-driven programming with multiple active objects called sprites.[8] Sprites can be drawn, as vector or bitmap graphics, from scratch in a simple editor that is part of Scratch, or can be imported from external sources.

The current version of Scratch does not treat procedures as first class structures and has limited file I/O options with Scratch 2.0 Extension Protocol; an experimental extension feature that allows interaction between Scratch 2.0 and other programs.[40] The Extension protocol allows interfacing with hardware boards such as Lego Mindstorms[41] or Arduino.[42] Scratch 3 only supports one-dimensional arrays, known as "lists", and floating point scalars and strings are supported, but with limited string manipulation ability. There is a strong contrast between the powerful multimedia functions and multi-threaded programming style and the rather limited scope of the Scratch programming language.

The source-code of Scratch and its derivatives are based on Squeak, which is based on Smalltalk-80. Version 2 of Scratch is implemented in ActionScript, with an experimental JavaScript-based interpreter being developed in parallel.[43]

A number of Scratch derivatives[44] called Scratch Modifications have been created using the source code of Scratch version 1.4. These programs are a variant of Scratch that normally include a few extra blocks[45] or changes to the GUI.

In July 2014, a program called ScratchJr was released for iPad. In 2016, ScratchJr was developed for Android. Although it was heavily inspired by Scratch and co-led by Mitch Resnick, the original creator of Scratch, it is nonetheless a complete rewrite designed for younger children.[46]

Some modifications additionally introduce shifts in underlying approach to computing, such as the language Snap!, featuring first class procedures (their mathematical foundations are called also lambda calculus), first class lists (including lists of lists), and first class truly object oriented sprites with prototyping inheritance, and nestable sprites, which are not part of Scratch.[47] Snap! (previously "BYOB") was developed by Jens Mönig[48][49] with documentation provided by Brian Harvey[50][51] from University of California, Berkeley and has been used to teach "The Beauty and Joy of Computing" introductory course in CS for non-CS-major students.[52]

See also[edit]

The following related youth computing projects also originated in the MIT Lifelong Kindergarten Group:

References[edit]

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External links[edit]