1.

Guess the outputs of the following codes:

Answer»
// Code 1:

function func1(){
setTimeout(()=>{
console.log(x);
console.log(y);
},3000);

var x = 2;
let y = 12;
}
func1();

// Code 2:

function func2(){
for(var i = 0; i < 3; i++){
setTimeout(()=> console.log(i),2000);
}
}
func2();

// Code 3:

(function(){
setTimeout(()=> console.log(1),2000);
console.log(2);
setTimeout(()=> console.log(3),0);
console.log(4);
})();

Answers:



  • Code 1 - Outputs 2 and 12. Since, even though let variables are not hoisted, due to the async nature of javascript, the complete function code runs before the setTimeout function. Therefore, it has access to both x and y.


  • Code 2 - Outputs 3, three times since variable declared with var keyword does not have block scope. Also, inside the for loop, the variable i is incremented first and then checked.


  • Code 3 - Output in the following order:

2
4
3
1 // After two seconds

Even though the second timeout function has a waiting time of zero seconds, the javascript engine always evaluates the setTimeout function using the Web API, and therefore, the complete function executes before the setTimeout function can execute.


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