Random string generator without repeating a combination

Question

I have tried to implement that the combinations are not repeated. in the image you can see how "sd" is repeated twice.

sd

const characters ='qwertyuiopasdfghjklzxcvbnm0987654321';

function generateString(length) {
    let result = ' ';
    const charactersLength = characters.length;
    for ( let i = 0; i < length; i++ ) {
        result += characters.charAt(Math.floor(Math.random() * charactersLength));
    }

    return result;
}



function captura(){
    lon=2;
    can=600;
    for (let i = 0; i < can; i++) {
        document.write(i+1 + ".- " + generateString(lon) + "<br>");
    }

}
captura();

Any help please?

Answer 1

Just save the results in a Set and make sure that what you return at the end isn't in the Set already.

const characters ='qwertyuiopasdfghjklzxcvbnm0987654321';

function generateString(length) {
    let result = ' ';
    const charactersLength = characters.length;
    for ( let i = 0; i < length; i++ ) {
        result += characters.charAt(Math.floor(Math.random() * charactersLength));
    }

    return result;
}
const set = new Set();
const generateUniqueString = (len) => {
  let str;
  do {
    str = generateString(len);
  } while (set.has(str));
  set.add(str);
  return str;
};


function captura(){
    for (let i = 0; i < 50; i++) {
        document.write(i+1 + ".- " + generateUniqueString(2) + '<br>');
    }

}
captura();

If you use this in a situation where you'll start getting anywhere near the limit of uniques, a better approach would be to generate all possible combinations in advance, randomize the array, then continually pop strings from the array when the function is called.