❓Что будет на выходе?

const sym1 = Symbol('description');
const sym2 = Symbol('description');

const obj = {
  [sym1]: 'value1',
  [sym2]: 'value2'
};

console.log(obj[sym1]);

Ответ:
'value1'

JavaScript test | #JavaScript & Max

❗️Что будет на выходе:

const regex = /a/g;
const str = 'banana';
console.log(str.match(regex));

Ответ: ['a', 'a']

JavaScript test | #JavaScript & Max

❗️Что будет на выходе:

const person = {
  name: 'Alice',
  greet() {
    return `Hello, I'm ${this.name}`;
  },
  farewell: () => `Goodbye from ${this.name}`
};

const greetFn = person.greet;
const farewellFn = person.farewell;

console.log(person.greet());
console.log(greetFn());
console.log(farewellFn());

Ответ: Hello, I'm Alice Hello, I'm undefined Goodbye from undefined

JavaScript test | #JavaScript & Max

❗️Что будет на выходе:

function processData({ a = 10, b = 20 } = { a: 30 }) {
  console.log(a, b);
}

processData({ a: 5 });
processData();

Ответ: 5 20 30 20


JavaScript test | #JavaScript & Max

❗️Что будет на выходе:

const team = {
  name: 'Eagles',
  players: ['Smith', 'Johnson', 'Williams'],
  coach: { name: 'Brown', experience: 12 },
  stats: { wins: 10, losses: 6 }
};

const { 
  name: teamName, 
  players: [firstPlayer, , thirdPlayer],
  coach: { name },
  stats: { wins, draws = 0 }
} = team;

console.log(`${teamName}-${firstPlayer}-${thirdPlayer}-${name}-${wins}-${draws}`);

Ответ:
Eagles-Smith-Williams-Brown-10-0


JavaScript test | #JavaScript & Max

❗️Что будет на выходе:

const createMathOps = (base) => {
  return {
    add: (x) => base + x,
    multiply: (x) => base * x
  };
};

const createAdvancedMathOps = (base) => {
  const basicOps = createMathOps(base);
  return {
    ...basicOps,
    square: () => basicOps.multiply(base),
    addThenSquare: (x) => {
      const added = basicOps.add(x);
      return added * added;
    }
  };
};

const calculator = createAdvancedMathOps(5);
console.log(calculator.addThenSquare(3));

Ответ: 64

JavaScript test | #JavaScript & Max

❗️Что будет на выходе:

try {
  try {
    // Creating a custom error type
    class CustomError extends Error {
      constructor(message) {
        super(message);
        this.name = "CustomError";
      }
    }
    
    const fn = () => {
      throw new CustomError("Something went wrong");
    };
    
    try {
      fn();
    } catch (e) {
      throw new TypeError("Type error occurred");
    }
  } catch (e) {
    console.log(e instanceof Error, e.name, e instanceof TypeError);
  }
} catch (e) {
  console.log("Outer catch", e.message);
}

Ответ: true 'TypeError' true

JavaScript test | #JavaScript & Max

❗️Что будет на выходе:

const person = {
  name: 'Alice',
  greet() {
    return `Hello, I'm ${this.name}`;
  },
  farewell: () => `Goodbye from ${this.name}`
};

const greetFn = person.greet;
const farewellFn = person.farewell;

console.log(person.greet());
console.log(greetFn());
console.log(farewellFn());

Ответ: Hello, I'm Alice Hello, I'm undefined Goodbye from undefined

JavaScript test | #JavaScript & Max

❗️Что будет на выходе:

const createMathOps = (base) => {
  return {
    add: (x) => base + x,
    multiply: (x) => base * x
  };
};

const createAdvancedMathOps = (base) => {
  const basicOps = createMathOps(base);
  return {
    ...basicOps,
    square: () => basicOps.multiply(base),
    addThenSquare: (x) => {
      const added = basicOps.add(x);
      return added * added;
    }
  };
};

const calculator = createAdvancedMathOps(5);
console.log(calculator.addThenSquare(3));

Ответ: 64

JavaScript test | #JavaScript & Max

❗️Что будет на выходе:

const memoryLeak = () => {
  const cache = new Map();
  const weakCache = new WeakMap();
  
  const objKey = { id: 123 };
  const data = { name: 'User data', value: 42 };
  
  cache.set(objKey, data);
  weakCache.set(objKey, data);
  
  // Simulate removing reference to key
  const result = { map: cache.has(objKey), weakMap: weakCache.has(objKey) };
  // objKey = null; // This would be an error, as const can't be reassigned
  
  return result;
};

console.log(memoryLeak());

Ответ: { map: true, weakMap: true }

JavaScript test | #JavaScript & Max

❗️Что будет на выходе:

const counter = (function () {
  let count = 0;
  const history = [];

  return {
    increment(step = 1) {
      count += step;
      history.push(count);
      return this;
    },
    decrement(step = 1) {
      count -= step;
      history.push(count);
      return this;
    },
    getHistory: () => history,
    getCount: () => count,
  };
})();

counter.increment(5).increment(3).decrement(2);

console.log(counter.getCount(), counter.getHistory().join(" -> "));

Ответ: 6 5 -> 8 -> 6

JavaScript test | #JavaScript & Max

❗️Что будет на выходе:

function greet(name) {
  return `Hello, ${name}!`;
}

function highlight(strings, ...values) {
  return strings.reduce((result, str, i) => {
    return result + str + (values[i] ? `<em>${values[i]}</em>` : '');
  }, '');
}

const user = 'Sarah';
const status = 'online';

console.log(highlight`User ${user} is currently ${status}.`);

Ответ: User <em>Sarah</em> is currently <em>online</em>.

JavaScript test | #JavaScript & Max

❗️Что будет на выходе:

function task1() {
  console.log('A');
  setTimeout(() => console.log('B'), 0);
  Promise.resolve().then(() => console.log('C'));
  Promise.resolve().then(() => setTimeout(() => console.log('D'), 0));
  Promise.resolve().then(() => console.log('E'));
  setTimeout(() => console.log('F'), 0);
  console.log('G');
}

task1();

Ответ: A G C E B F D


JavaScript test | #JavaScript & Max

❗️Что будет на выходе:

const obj = {
   x: 10,
   foo() {
      setTimeout(function() {
         console.log(this.x);
      }, 1000);
   }
};
obj.foo();

Ответ: undefined

JavaScript test | #JavaScript & Max

❗️Что будет на выходе:

function highlight(strings, ...values) {
  return strings.reduce((result, str, i) => {
    const value = values[i] ? `<span>${values[i]}</span>` : '';
    return result + str + value;
  }, '');
}

const language = 'JavaScript';
const years = 10;

const result = highlight`I have been coding in ${language} for ${years} years`;
console.log(result);

Ответ: I have been coding in <span>JavaScript</span> for <span>10</span> years


JavaScript test | #JavaScript & Max

❗️Что будет на выходе:

function* generator1() {
  yield 1;
  yield 2;
}

function* generator2() {
  yield* generator1();
  yield 3;
}

const gen = generator2();
console.log(gen.next().value);
console.log(gen.next().value);
console.log(gen.next().value);

Ответ: 1, 2, 3

JavaScript test | #JavaScript & Max

❗️Что будет на выходе:

const createMathOps = (base) => {
  return {
    add: (x) => base + x,
    multiply: (x) => base * x
  };
};

const createAdvancedMathOps = (base) => {
  const basicOps = createMathOps(base);
  return {
    ...basicOps,
    square: () => basicOps.multiply(base),
    addThenSquare: (x) => {
      const added = basicOps.add(x);
      return added * added;
    }
  };
};

const calculator = createAdvancedMathOps(5);
console.log(calculator.addThenSquare(3));

Ответ: 64

JavaScript test | #JavaScript & Max

❗️Что будет на выходе:

function* infiniteGenerator() {
  let i = 0;
  while (true) {
    yield i++;
  }
}

const weakMap = new WeakMap();
const gen = infiniteGenerator();

weakMap.set(gen, gen.next().value);

const result = weakMap.get(gen) + gen.next().value;

console.log(result);

Ответ: 1


JavaScript test | #JavaScript & Max

❗️Что будет на выходе:

function highlight(strings, ...values) {
  return strings.reduce((result, str, i) => {
    const value = values[i] ? `<span>${values[i]}</span>` : '';
    return result + str + value;
  }, '');
}

const language = 'JavaScript';
const years = 10;

const result = highlight`I have been coding in ${language} for ${years} years`;
console.log(result);

Ответ: I have been coding in <span>JavaScript</span> for <span>10</span> years


JavaScript test | #JavaScript & Max

❗️Что будет на выходе:

function analyze(...items) {
  const [first, ...rest] = items;
  const { length } = [...rest, 'bonus'];
  const result = {
    ...first,
    count: length,
  };
  
  console.log(result);
}

analyze({ id: 42, name: 'Item' }, 'a', 'b');

Ответ: { id: 42, name: 'Item', count: 3 }

JavaScript test | #JavaScript & Max