Why is string.replace() not working inside the function when it works perfectly outside of it?

Question

I'm trying to replace the "..." in a given string with other different strings stored into an array using this function:

`

function addTokens(input, tokens) 
{
  let returnInput = input;

  if ((typeof input === 'string') || (input instanceof String)) 
  { 
      if(input.length >= 6)
      {
          for (let i = 0; i < tokens.length; i++) 
          {
              if((tokens[i].tokenName === 'string') || (tokens[i].tokenName instanceof String))
              {
                  returnInput = returnInput.replace("...",`${tokens[i].tokenName}`);
              }   
              else
              {
                  //throw new Error("Invalid array format");
              }
          }
      }
      else
      {
          //throw new Error("Input should have at least 6 characters"); 
      } 
  }
  else
  {
      //throw new Error("Input should be a string");
  } 

  return returnInput;
}

`

I have even commented the errors so that they don't interfere in any way, but it doesn't seem to work; if I call

result = addTokens('User ...', [{ tokenName: 'user' }])
console.log(result)

, it just returns the initial "User ..." instead of the "User ${user}" I want it to.

However, when I run this little bit of code:

`

let str = "User ...";
let tok = [{ tokenName: "user" }]
str = str.replace("...", `${tok[0].tokenName}`);
console.log(str);

`

by itself, it does exactly what I intend it to do.

Can anyone help me find out what the issue is? Sorry for any rookie mistakes, I'm new to Javascript. Thanks!

Your if-statement is never true. `"user" instanceof String` is `false` not `true` — Nick Parsons, Nov 20 '22 at 00:00

score 0 · Accepted Answer · answered Nov 20 '22 at 00:01

You have a typo:

(tokens[i].tokenName === 'string')

should be

(typeof tokens[i].tokenName === 'string')

With that updated, here is the working code:

function addTokens(input, tokens) 
{
  let returnInput = input;

  if ((typeof input === 'string') || (input instanceof String)) 
  { 
      if(input.length >= 6)
      {
          for (let i = 0; i < tokens.length; i++) 
          {
              if((typeof tokens[i].tokenName === 'string') || (tokens[i].tokenName instanceof String))
              {
                  returnInput = returnInput.replace("...",`${tokens[i].tokenName}`);
              }   
              else
              {
                  //throw new Error("Invalid array format");
              }
          }
      }
      else
      {
          //throw new Error("Input should have at least 6 characters"); 
      } 
  }
  else
  {
      //throw new Error("Input should be a string");
  } 

  return returnInput;
}

result = addTokens('User ...', [{ tokenName: 'user' }])
console.log(result)

Thank you very much! I can't believe I didn't notice that – Gabriel Onicala Nov 20 '22 at 00:13 — Gabriel Onicala, Nov 20 '22 at 00:13

Why is string.replace() not working inside the function when it works perfectly outside of it?

1 Answers1