CHALLENGE
class Logger {
log(msg) {
return `[LOG]: ${msg}`;
}
}
class Formatter {
format(text) {
return text.toUpperCase();
}
}
class Service {
constructor(logger, formatter) {
this.logger = logger;
this.formatter = formatter;
}
process(data) {
const formatted = this.formatter.format(data);
return this.logger.log(formatted);
}
}
const service = new Service(new Logger(), new Formatter());
console.log(service.process('hello world'));❤4👍3🤔1
What is the output?
Anonymous Quiz
50%
[LOG]: HELLO WORLD
29%
HELLO WORLD
14%
hello world
8%
[LOG]: hello world
❤1
CHALLENGE
let obj1 = { name: 'Sarah' };
let obj2 = { name: 'Mike' };
obj1.ref = obj2;
obj2.ref = obj1;
let weakRef = new WeakRef(obj1);
let registry = new FinalizationRegistry((value) => {
console.log(`Cleanup: ${value}`);
});
registry.register(obj1, 'obj1-cleaned');
obj1 = null;
obj2 = null;
console.log(weakRef.deref()?.name || 'undefined');
console.log('Script completed');What is the output?
Anonymous Quiz
31%
Sarah Script completed
40%
undefined Script completed Cleanup: obj1-cleaned
20%
Sarah Script completed Cleanup: obj1-cleaned
9%
undefined Script completed
🔥4🤔3❤1
CHALLENGE
class EventEmitter {
constructor() {
this.events = {};
}
on(event, callback) {
this.events[event] = this.events[event] || [];
this.events[event].push(callback);
return this;
}
emit(event, data) {
if (this.events[event]) {
this.events[event].forEach(cb => cb(data));
}
return this;
}
}
const emitter = new EventEmitter();
emitter.on('test', x => console.log(x * 2))
.on('test', x => console.log(x + 5))
.emit('test', 10);❤7
Back in May 1995, a 33 year old Brendan Eich built the first prototype of JavaScript in just ten days, originally codenamed Mocha (and then LiveScript). On December 4, 1995, Netscape and Sun Microsystems officially announced 'JavaScript' in a press release as "an easy-to-use object scripting language designed for creating live online applications that link together objects and resources on both clients and servers."
Over thirty years, JavaScript has cemented its place at the heart of the Web platform, and more broadly in desktop apps, operating systems (e.g. Windows' use of React Native), mobile apps, and even on microcontrollers.
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❤13👍4🤔1
CHALLENGE
const map = new Map([
['a', 1],
['b', 2],
['c', 3]
]);
const key = { id: 'key' };
map.set(key, 4);
map.set(key, 5);
const result = [];
result.push(map.get('a'));
result.push(map.get(key));
result.push(map.size);
result.push(map.has({ id: 'key' }));
console.log(result);
What is the output?
Anonymous Quiz
31%
[1, 5, 4, true]
28%
[1, 4, 4, false]
27%
[1, 5, 4, false]
14%
[1, 5, 5, true]
❤2👍2🔥2🤔1
CHALLENGE
const promise1 = Promise.resolve(10);
const promise2 = promise1.then(x => x * 2);
const promise3 = promise2.then(x => {
console.log(x);
return x + 5;
});
const promise4 = promise2.then(x => {
console.log(x);
return x * 3;
});
Promise.all([promise3, promise4]).then(results => {
console.log(results);
});
What is the output?
Anonymous Quiz
41%
20 20 [25, 60]
23%
10 10 [15, 30]
19%
10 20 [25, 60]
17%
20 25 [25, 60]
❤3👍3🤔2🤩2
CHALLENGE
const x = 5;
const y = 10;
const obj = {
x,
y,
z: x + y,
calculate() {
return this.x * this.y;
},
[x + y]: 'computed'
};
console.log(obj.calculate() + obj[15] + obj.z);
❤1
❤9
CHALLENGE
const curry = (fn) => {
return function curried(...args) {
if (args.length >= fn.length) {
return fn.apply(this, args);
}
return (...nextArgs) => curried(...args, ...nextArgs);
};
};
const multiply = (a, b, c) => a * b * c;
const curriedMultiply = curry(multiply);
const step1 = curriedMultiply(2);
const step2 = step1(3);
const result = step2(4);
console.log(result);👍1