Upload part 0

part0/0.4.md

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+# Exercise 0.4
+
+```mermaid
+sequenceDiagram
+    participant browser
+    participant server
+
+    Note right of browser: User enters new note entry and click "Save"
+
+    browser->>server: HTTP POST https://studies.cs.helsinki.fi/exampleapp/new_note
+    activate server
+
+    Note left of server: New note entry is added
+
+    server-->>browser: Redirect to https://studies.cs.helsinki.fi/exampleapp/notes
+    deactivate server
+
+    browser->>server: HTTP GET https://studies.cs.helsinki.fi/exampleapp/main.css
+    activate server
+    server-->>browser: main.css
+    deactivate server
+
+    browser->>server: HTTP GET https://studies.cs.helsinki.fi/exampleapp/main.js
+    activate server
+    server-->>browser: main.js
+    deactivate server
+
+    Note right of browser: The browser starts executing the JavaScript code that fetches the JSON from the server
+
+    browser->>server: HTTP GET https://studies.cs.helsinki.fi/exampleapp/data.json
+    activate server
+    server-->>browser: [{ "content": "HTML is easy", "date": "2023-1-1" }, ... ]
+    deactivate server
+
+    Note right of browser: The browser executes the callback function that renders the notes
+
+```