How do I do a function with if/Else?

Question

I wrote this function more gives error and I would like to understand why:

function hojeSeJoga (domingo){
  if (domingo==domingo){
    console.log("Hoje é dia de futebol")
    return true;
    } else{
      console.log("Hoje não é dia de futebol")
      return false;
      } 
  }

Answer 1

You should use quotes to make this comparison. I also suggest you change the name of the function parameter to day:

function hojeSeJoga (dia){
  if (dia=="domingo"){
    console.log("Hoje é dia de futebol")
    return true;
  }else{
    console.log("Hoje não é dia de futebol")
     return false;
    } 
 }
 
 hojeSeJoga('sábado')
 hojeSeJoga('domingo')

In its original code, you do not use quotation marks, which makes the function think that the right operand of the equality operator is a variable: thus, the comparison is being if something is equal to this something, that is, it always enters the first if, independent of the value of the argument passed to the function.