Docker 'Bind for 0.0.0.0:8080 failed: port is already allocated' Fix
Fix Docker 'port is already allocated' and 'address already in use': find the container or process on the port, then remap or bind to 127.0.0.1.
~7 min readread →
Developer interview notes & guides — Page 12
Focused explanations and longer guides, with worked scenarios, common mistakes and interview exercises across every chapter.
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Showing 265–288 of 825 articles
Git: Your branch and 'origin/main' have diverged (Fix)
Fix 'Your branch and origin/main have diverged' and fatal: Need to specify how to reconcile divergent branches: merge, rebase or ff-only.
~7 min readread →
Git: failed to push some refs (fetch first, non-fast-forward)
Fix Git's error: failed to push some refs and ! [rejected] main -> main (fetch first): fetch, rebase or merge, and force-with-lease safely.
~7 min readread →
Git Permission denied (publickey) on GitHub: SSH Fix
Fix git@github.com: Permission denied (publickey) and Could not read from remote repository: test SSH, load keys, set IdentityFile, or use HTTPS.
~7 min readread →
Git fatal: refusing to merge unrelated histories (How to Fix)
Fix Git's fatal: refusing to merge unrelated histories: why it happens, when --allow-unrelated-histories is right, and safer alternatives.
~8 min readread →
How to Undo the Last Commit in Git: reset, amend, revert
How to undo the last commit in Git: git reset --soft, --mixed or --hard, commit --amend, git revert for pushed commits, and reflog recovery.
~7 min readread →
ClassNotFoundException vs NoClassDefFoundError in Java
ClassNotFoundException vs NoClassDefFoundError in Java: what each error means, why classes go missing at runtime and how to fix the classpath.
~8 min readread →
Java ConcurrentModificationException: Removing Items Safely
Fix java.util.ConcurrentModificationException when removing items in a loop: use removeIf or Iterator.remove, and see when concurrent lists help.
~7 min readread →
Java NullPointerException: Reading the Message and Fixing the Cause
Fix java.lang.NullPointerException by reading the helpful message, finding the null in the top stack frame and validating inputs early.
~8 min readread →
java.lang.OutOfMemoryError: Java Heap Space: Diagnosis and Fixes
Fix java.lang.OutOfMemoryError: Java heap space by checking -Xmx, capturing a heap dump and finding what retains memory in Eclipse MAT.
~8 min readread →
UnsupportedClassVersionError: Class File Version Mismatch in Java
Fix UnsupportedClassVersionError (class file version 65.0 vs 61.0) by matching the runtime JDK to your build or compiling with javac --release.
~8 min readread →
UnsupportedOperationException from Arrays.asList and List.of
Why Arrays.asList and List.of throw UnsupportedOperationException on add or remove, and how to choose a mutable copy or an immutable list.
~6 min readread →
JavaScript Array Sort Comparators
Sort arrays in place with a correct comparator, understand default string ordering and sort stability, and avoid the numeric and string traps.
~3 min readread →
JavaScript Async Iteration and Backpressure
Consume async generators with for await, propagate errors and pace a producer to a slow consumer without buffering the whole stream.
~3 min readread →
Fixing 'Blocked by CORS Policy' Errors in JavaScript fetch
Fix 'blocked by CORS policy' fetch errors: which headers the server must send, preflights, credentials, dev proxies and why no-cors fails.
~8 min readread →
TypeError: Cannot Read Properties of Undefined in JavaScript
Fix TypeError: Cannot read properties of undefined by finding which value is missing, reading the stack trace and repairing the data flow.
~8 min readread →
Cannot Use Import Statement Outside a Module: ESM vs CommonJS
Fix SyntaxError: Cannot use import statement outside a module in Node and browsers: type module, .mjs, require of ESM and __dirname in ESM.
~8 min readread →
JavaScript Custom Error Classes
Extend Error to carry a stable name and instanceof, preserve the underlying cause, and avoid the string-throwing mistakes interviewers look for.
~3 min readread →
TypeError: x Is Not a Function in JavaScript: Causes and Fixes
Fix TypeError: x is not a function in JavaScript: wrong imports, shadowed names, lost this, a missing semicolon or .map on a non-array.
~7 min readread →
RangeError: Maximum Call Stack Size Exceeded in JavaScript
Fix RangeError: Maximum call stack size exceeded: missing base cases, self-calling setters, circular data, huge spreads and deep recursion.
~8 min readread →
JavaScript Proxy Traps for Validation
Validate object writes with Proxy set and get traps, forward with Reflect and avoid the invariants that make a proxy lie about its target.
~3 min readread →
ReferenceError: x Is Not Defined vs undefined in JavaScript
Fix ReferenceError: x is not defined: typos, block scope, the TDZ, window or require missing in Node, and scripts that load in the wrong order.
~7 min readread →
JavaScript structuredClone and Transferables
Deep-clone Dates, Maps, Sets and cyclic graphs with structuredClone, and move ArrayBuffers between contexts instead of copying them.
~3 min readread →
SyntaxError: Unexpected Token '<' in JSON: Debugging fetch
Fix SyntaxError: Unexpected token '<' in JSON from fetch: the server sent HTML. Check res.ok and content-type, then read the body as text.
~7 min readread →
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