Generate a random string in JavaScript In a short and fast way!

Random-string

 //http://stackoverflow.com/questions/105034/how-to-create-a-guid-uuid-in-javascript
 Math.random().toString(36).substring(2, 15) + Math.random().toString(36).substring(2, 15);

  const idString = async (string_length) => {
    var random_str = "";
    var characters =
      "ABCDEFGHIJKLMNOPQRSTUVWXYZqeytrpolkadjsghfgmnbzxcvnQPOWEYRKASJHDGFMNBCVX--___-_jsfhrlg-_124903564576986483658fgh4sdfh687e4h897WETHJ68F7G4688471877GFHJFFGJ87469857468746hfghwrtiyj4598yhdjkhgnk";
    for (let index = 0; index < string_length; index++) {
      random_str += characters.charAt(
        Math.floor(Math.random() * characters.length)
      );
    }
    let string = `${random_str}`;
    console.log(string);
    return string;
  };

@zeelkakdiya constructive feedback to improve this code:

1. This is not an async function, it does not use promises
2. var is used rather than let and in some cases const are more appropriate
3. let string does not need ${}
4. console.log is not useful in production code and actually slows down this function
5. let string to return could be removed.
6. casing is inconsistent

const generateID = (stringLength = 20) => {
    let randomStr = "";
    const characters = "ABCDEFGHIJKLMNOPQRSTUVWXYZqeytrpolkadjsghfgmnbzxcvnQPOWEYRKASJHDGFMNBCVX--___-_jsfhrlg-_124903564576986483658fgh4sdfh687e4h897WETHJ68F7G4688471877GFHJFFGJ87469857468746hfghwrtiyj4598yhdjkhgnk";
    for (let index = 0; index < stringLength; index++) {
      randomStr += characters.charAt(
        Math.floor(Math.random() * characters.length)
      );
    }
    return randomStr;
  };