Pick a random letter from string in JavaScript

问题:

This question is different from Take random letters out from a string because I am not trying to remove anything from the string.

I'm trying to pick a random letter from a string in JavaScript using Math.floor(Math.random()* string.length) and a while loop. It needs to continually add new random letters to this string until a specified length.

My code is:

var emptyString = "";
var alphabet = "abcdefghijklmnopqrstuvwxyz";
var getRandomLetter = alphabet[Math.floor(Math.random() * alphabet.length)];
var randomLetter = getRandomLetter;

while (emptyString.length < 6) {
emptyString += randomLetter;
emptyString ++;
} 
console.log(emptyString);

Problems: The output is the same letter 6 times: ex. pppppp

The random letter is generated from the string only once and then repeated until the specified length. I need it to generate random output for each letter: ex. pwezjm

I also noticed that if I do a second different while loop over the string it will generate the same output as the first loop: ex. pppppp

I thought it would at least generate a different random letter then the first loop but it does not. Why is that?

回答1:

Because you should obtain the letter every time, but you do it just once.

var emptyString = "";
var alphabet = "abcdefghijklmnopqrstuvwxyz";

while (emptyString.length < 6) {
  emptyString += alphabet[Math.floor(Math.random() * alphabet.length)];
} 
console.log(emptyString);

Also, not sure what you wanted to achieve with emptyString++, removing that, since ++ is the "increment by one" operator and you can't incremenent a string. I think the purpose was to have it as a counter for that while loop, but it's needless, since the counter is the string length already.

回答2:

Get the random character in a loop

In your example, you are obtaining random character from array only once hence there is no way you are going to get another random character in while loop

Also note that emptyString++ will cause result as NaN as you are trying to post-increment the string

var emptyString = "";
var alphabet = "abcdefghijklmnopqrstuvwxyz";

while (emptyString.length < 6) {
  emptyString += alphabet[Math.floor(Math.random() * alphabet.length)];
}
console.log(emptyString);

Another tip, alphabet.length could be cached instead of asking for it every time in while

回答3:

While those above are nice. I like shorter code.

const randomLetter = ('abcdefghijklmnopqrstuvwxyz').split('')[(Math.floor(Math.random() * 26 ))];

回答4:

You need to change getRandomLetter into a function, and reassign randomLetter inside the loop like this:

var emptyString = "";
var alphabet = "abcdefghijklmnopqrstuvwxyz";
function getRandomLetter() {
  return alphabet[Math.floor(Math.random() * alphabet.length)];
}
var randomLetter;

while (emptyString.length < 6) {
  randomLetter = getRandomLetter();
  emptyString += randomLetter;
} 
console.log(emptyString);

You also can't increment emptyString, since it is a string.