Guess the Output

Think like the JS engine. Can you predict what will be logged to the console?

Q1: Hoisting

console.log(a);
var a = 5;

• Answer: undefined. (var is hoisted but not its assignment).

Q2: Closures

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

• Answer: 3, 3, 3. (Because var is function-scoped. Use let to fix it).

Q3: Equality

console.log([] == []);
console.log([] === []);

• Answer: false, false. (Arrays are compared by reference, and these are two different objects).

Q4: Coercion

console.log(1 + "2" + 3);

• Answer: "123". (Num 1 + Str "2" = Str "12". Str "12" + Num 3 = Str "123").

Next Step: Prepare for Machine Coding. in interviews to guess the output.