LEVEL-1-CROSS-CONCEPT-QUESTIONS.md

🎯 Level 1 Cross-Concept Interview Questions

🚨 CRITICAL: These questions test MULTIPLE concepts simultaneously

Each question combines 2-4 Level 1 concepts to simulate real-world complexity and interview scenarios.

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🔥 Question Set 1: Hoisting + Scopes + Closures

Q1: The Infamous Loop Closure Problem

for (var i = 0; i < 3; i++) {
  setTimeout(function() {
    console.log(i);
  }, 1000);
}

What will be logged and why?

• Tests: Hoisting, Scopes, Closures, Event Loop
• Answer: All logs will show 3 due to closure capturing the reference to i, not the value

Q2: Let vs Var in Loops with Closures

for (let i = 0; i < 3; i++) {
  setTimeout(function() {
    console.log(i);
  }, 1000);
}

What will be logged and why?

• Tests: Block scope, Temporal Dead Zone, Closures, Event Loop
• Answer: 0, 1, 2 because let creates block scope for each iteration

Q3: Function Declaration vs Expression in Closures

var x = 10;

function outer() {
  var x = 20;
  
  function inner() {
    console.log(x);
  }
  
  return inner;
}

var fn = outer();
fn();

What will be logged and why?

• Tests: Hoisting, Scopes, Closures, Lexical scoping
• Answer: 20 due to lexical scoping and closure capturing the x from outer's scope

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🔥 Question Set 2: This + Scopes + Closures

Q4: This Context Loss in Closures

var name = "Global";

var obj = {
  name: "Object",
  getName: function() {
    return function() {
      return this.name;
    };
  }
};

console.log(obj.getName()());

What will be logged and why?

• Tests: This keyword, Context loss, Closures, Global scope
• Answer: "Global" because the returned function loses its this context and defaults to global

Q5: Arrow Functions Preserving This

var name = "Global";

var obj = {
  name: "Object",
  getName: function() {
    return () => {
      return this.name;
    };
  }
};

console.log(obj.getName()());

What will be logged and why?

• Tests: Arrow functions, This binding, Closures, Lexical scoping
• Answer: "Object" because arrow functions preserve the this context from their enclosing scope

Q6: Method Assignment Context Loss

var name = "Global";

var obj = {
  name: "Object",
  getName: function() {
    return this.name;
  }
};

var getNameFn = obj.getName;
console.log(getNameFn());

What will be logged and why?

• Tests: This keyword, Context loss, Method context, Global scope
• Answer: "Global" because getNameFn is called in global context, losing the object context

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🔥 Question Set 3: Event Loop + Closures + Scopes

Q7: Async Closures with Var

for (var i = 0; i < 3; i++) {
  (function(j) {
    setTimeout(function() {
      console.log(j);
    }, j * 1000);
  })(i);
}

What will be logged and when?

• Tests: Event Loop, Closures, IIFE, Scopes, setTimeout
• Answer: 0 immediately, 1 after 1 second, 2 after 2 seconds due to IIFE creating new scope for each iteration

Q8: Promise Microtasks vs setTimeout

console.log('1');

setTimeout(() => {
  console.log('2');
}, 0);

Promise.resolve().then(() => {
  console.log('3');
});

console.log('4');

What will be the output order and why?

• Tests: Event Loop, Microtasks, Macrotasks, Call Stack
• Answer: 1, 4, 3, 2 because microtasks (Promises) have priority over macrotasks (setTimeout)

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🔥 Question Set 4: All Concepts Combined

Q9: The Ultimate Challenge

var name = "Global";
var counter = 0;

function createCounter() {
  var counter = 0;
  
  return {
    increment: function() {
      counter++;
      return counter;
    },
    getValue: function() {
      return counter;
    }
  };
}

var counter1 = createCounter();
var counter2 = createCounter();

console.log(counter1.increment()); // ?
console.log(counter1.increment()); // ?
console.log(counter2.increment()); // ?
console.log(counter1.getValue()); // ?
console.log(counter2.getValue()); // ?

What will be logged and why?

• Tests: ALL Level 1 concepts combined
• Answer: 1, 2, 1, 2, 1 due to closures creating separate counter variables for each instance

Q10: Complex Scope Chain

var x = 1;

function outer() {
  var x = 2;
  
  function inner() {
    var x = 3;
    
    setTimeout(function() {
      console.log(x);
    }, 1000);
  }
  
  inner();
}

outer();

What will be logged and why?

• Tests: Scope chain, Closures, Event Loop, Variable shadowing
• Answer: 3 because the closure captures the x from the inner function's scope

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🎯 Interview Question Types

Type 1: Code Output Prediction

• Given code, predict the output
• Explain the reasoning step by step
• Identify which concepts are at play

Type 2: Bug Identification

• Find bugs in given code
• Explain why they occur
• Provide solutions

Type 3: Code Writing

• Write code that demonstrates specific concept interactions
• Implement solutions to common problems
• Show understanding of best practices

Type 4: Concept Explanation

• Explain how multiple concepts work together
• Describe real-world scenarios
• Discuss trade-offs and alternatives

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🚀 Practice Strategy

1. Start Simple: Begin with questions combining 2 concepts
2. Build Complexity: Gradually add more concepts
3. Time Yourself: Practice under interview conditions
4. Explain Aloud: Verbalize your reasoning process
5. Draw Diagrams: Visualize scope chains and execution flow
6. Multiple Solutions: Find different ways to solve the same problem

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