Why is my criteria inside IF not working?

Question

Even though I enter the exact same input as the criteria, the code still doesn't run properly.

--> Link to the CodePen of this error <--

let addOrRem = String(prompt("Do you want to add or remove any content? (add/rem)").trim().toLocaleLowerCase());

    if(addOrRem !== "rem" || addOrRem !== "add") {
            alert("Invalid answer, try again!");
    }

If I write the exact same code in a bundled way, the criteria works properly...

--> Link to the CodePen of this error partially solved <--

let addOrRem = String(prompt("Do you want to add or remove any content? (add/rem)").trim().toLocaleLowerCase());

    if(addOrRem !== "rem") {
      if(addOrRem !== "add"){
        alert("Invalid answer, try again!");
      }    
    }

I was expecting the first code to give the exact same output as the second one. I tried switching it for function "while" but resulted in the same issue.

Answer 1

That's because your condition should actually be an AND, not an OR.

if (addOrRem !== "rem" && addOrRem !== "add")

Consider the fact that addOrRem can only be equal to one value, so one of addOrRem !== "rem" and addOrRem !== "add" will always be true (and thus the entire condition will always be true with ||). addOrRem cannot be simultaneously equal to both "rem" and "add", which is required for your original condition to be false.