What is the output?
Anonymous Quiz
32%
10 18 false true 198
34%
5 9 false true 198
30%
10 9 false true Property "_secret" not found
3%
10 9 true false 198
CHALLENGE
class Range {
constructor(start, end, step = 1) {
this.start = start;
this.end = end;
this.step = step;
}
[Symbol.iterator]() {
let current = this.start;
const { end, step } = this;
return {
next() {
if (current <= end) {
const value = current;
current += step;
return { value, done: false };
}
return { value: undefined, done: true };
}
};
}
}
const range = new Range(1, 10, 3);
const result = [...range].map(n => n ** 2);
console.log(result);
❤4
What is the output?
Anonymous Quiz
19%
[ 1, 9, 25, 49 ]
53%
[ 1, 16, 49, 100 ]
16%
[ 1, 9, 49 ]
12%
[ 1, 9, 25, 49, 81 ]
❤4🤔1
CHALLENGE
const p1 = new Promise((resolve) => {
console.log("A");
resolve("B");
});
const p2 = p1.then((val) => {
console.log(val);
return "C";
});
p2.then((val) => console.log(val));
console.log("D");
❤4🤔2
CHALLENGE
class EventEmitter {
#listeners = new Map();
on(event, listener) {
if (!this.#listeners.has(event)) {
this.#listeners.set(event, []);
}
this.#listeners.get(event).push(listener);
return this;
}
emit(event, ...args) {
const handlers = this.#listeners.get(event) ?? [];
handlers.forEach(fn => fn(...args));
return this;
}
}
const emitter = new EventEmitter();
const log = [];
emitter
.on("data", val => log.push(`A:${val}`))
.on("data", val => log.push(`B:${val * 2}`))
.on("end", () => log.push("done"));
emitter.emit("data", 5).emit("data", 3).emit("end");
console.log(log.join(","));
👍1
What is the output?
Anonymous Quiz
36%
A:5,B:10,A:3,B:6,done
39%
A:5,A:3,B:6,B:10,done
21%
A:5,B:10,done,A:3,B:6
3%
A:5,B:25,A:3,B:9,done
❤3
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❤4👍1🔥1
npm is the only major package manager that runs dependency install scripts (e.g. postinstall) by default, and they’ve become too much of a security weakness, says Jamie, who works for GitHub (maintainers of npm). This RFC features further discussion of the idea and the tradeoffs involved.
Jamie Magee
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❤3
CHALLENGE
const createModule = (() => {
const privateCache = new WeakMap();
return function(name) {
const state = { name, version: 1, active: true };
privateCache.set(state, { accessCount: 0 });
return {
getInfo() {
const meta = privateCache.get(state);
meta.accessCount++;
return `${state.name}@v${state.version}`;
},
getAccessCount() {
return privateCache.get(state).accessCount;
},
upgrade() {
state.version++;
return this;
}
};
};
})();
const mod = createModule("auth");
mod.upgrade().upgrade();
console.log(mod.getInfo());
console.log(mod.getAccessCount());
❤2👍2