merge dev into main (extended topics)

Author: DucMinhNe

topics/array-methods/README.md

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+# Array Methods
+
+Array methods are the workhorses of JS.
+
+## Key points
+
+- non-mutating: map, filter, reduce, find, slice, concat, flat, flatMap
+- mutating: push, pop, shift, unshift, splice, sort, reverse
+- search: includes, indexOf, findIndex
+- test: every, some
+
+## Examples
+
+See `examples/` for runnable demos.
+
+## Exercise
+
+Implement Array#flatten without using `flat()`.

topics/array-methods/examples/01-array-methods.js

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+const a = [1, 2, 3, 4, 5];
+
+console.log(a.map(x => x * 2));            // [2,4,6,8,10]
+console.log(a.filter(x => x % 2 === 0));   // [2,4]
+console.log(a.reduce((acc, x) => acc + x, 0)); // 15
+console.log(a.find(x => x > 3));           // 4
+console.log(a.findIndex(x => x > 3));      // 3
+console.log(a.every(x => x > 0));          // true
+console.log(a.some(x => x > 4));           // true
+console.log(a.includes(3));                // true
+
+console.log([1, [2, [3, [4]]]].flat(2));   // [1,2,3,[4]]
+console.log([1, 2].flatMap(x => [x, x*10])); // [1,10,2,20]
+
+// careful: sort default is string compare
+console.log([10, 1, 2].sort());            // [1, 10, 2]
+console.log([10, 1, 2].sort((a, b) => a - b)); // [1, 2, 10]

topics/array-methods/exercise.js

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+// Exercise: Implement Array#flatten without using `flat()`.
+// TODO: implement
+module.exports = {};

topics/assert-module/README.md

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+# assert module
+
+Built-in assertions for quick checks and tests.
+
+## Key points
+
+- `assert.strictEqual(a, b)` — like ===
+- `assert.deepStrictEqual(a, b)` — recursive structural
+- `assert.throws(fn, /msg/)` — confirms an error
+- `assert.rejects(promise)` for async
+
+## Examples
+
+See `examples/` for runnable demos.
+
+## Exercise
+
+Replace 5 ad-hoc throws with `assert` calls.

topics/assert-module/examples/01-assert.js

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+const assert = require('node:assert/strict');
+
+assert.equal(1 + 1, 2);
+assert.deepEqual([1, 2, 3], [1, 2, 3]);
+assert.deepStrictEqual({ a: 1 }, { a: 1 });
+assert.notEqual(1, 2);
+assert.ok(true);
+
+assert.throws(() => { JSON.parse('{'); }, SyntaxError);
+
+assert.rejects(async () => { throw new Error('x'); }, { message: 'x' });

topics/assert-module/exercise.js

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+// Exercise: Replace 5 ad-hoc throws with `assert` calls.
+// TODO: implement
+module.exports = {};

topics/buffer-deep/README.md

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+# Buffer
+
+Node's binary data buffer (fixed-length, like Uint8Array).
+
+## Key points
+
+- `Buffer.from(...)`, `Buffer.alloc(n)`, `Buffer.allocUnsafe(n)`
+- convert with `.toString('utf8' | 'hex' | 'base64')`
+- Buffer is a subclass of Uint8Array
+- concat with `Buffer.concat([...])`
+
+## Examples
+
+See `examples/` for runnable demos.
+
+## Exercise
+
+Read a file into a Buffer and print its hex digest.

topics/buffer-deep/examples/01-buffer.js

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+const buf = Buffer.from('hello', 'utf8');
+console.log(buf);              // <Buffer 68 65 6c 6c 6f>
+console.log(buf.length);       // 5
+console.log(buf.toString('hex'));    // '68656c6c6f'
+console.log(buf.toString('base64')); // 'aGVsbG8='
+
+const a = Buffer.from('a');
+const b = Buffer.from('b');
+console.log(Buffer.concat([a, b]).toString());
+
+// allocUnsafe doesn't zero — faster but you must overwrite
+const u = Buffer.allocUnsafe(4);
+u.fill(0);
+console.log(u);
+
+const json = JSON.parse(Buffer.from('{"k":1}').toString());
+console.log(json);

topics/buffer-deep/exercise.js

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+// Exercise: Read a file into a Buffer and print its hex digest.
+// TODO: implement
+module.exports = {};

topics/console-deep/README.md

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+# console module
+
+Beyond console.log: log, info, warn, error, group, time, trace, dir, table.
+
+## Key points
+
+- `console.error` writes to stderr (separate stream)
+- `console.time / timeEnd` for quick timing
+- `console.table(rows)` prints aligned rows
+- `new console.Console(stdout, stderr)` builds a custom logger
+
+## Examples
+
+See `examples/` for runnable demos.
+
+## Exercise
+
+Use console.table to format an array of users.