如何将特定字符串转换为数组中的特定数字？

Question

I'm looking for a way to convert a string to a number. I'm making a rock paper scissors game for class, and I am not allowed to use custom functions. I want to convert the variable userChoice from "rock", "paper", and "scissors" to 0, 1, and 2, respectively. Here's the code in question:

    const options = [`rock`, `paper`, `scissors`];
    alert (`Let's play Rock, Paper, Scissors!`);
    let userChoice =  prompt (`Please enter your choice (rock, paper, or scissors`);
    let compChoice =  Math.floor((Math.random() * 3));
    let inputValid = null

if ((userChoice == `rock`) || (userChoice == `paper`) || (userChoice == `scissors`)) {
inputValid = true
}

else {
  inputValid = false
}

if (( userChoice )


    
    let dialogChoice = (`You chose ${userChoice}! The computer chose ${compChoice}!`)

let dialogUserWin = `User wins!`
let dialogCompWin = `Computer wins!`
let dialogTie     = `It's a tie!`
let dialogReplay = `Press F5 to play again`

console.log(compChoice)

//I could always do something like:

if (userChoice = `rock`) {
userChoice = 0}
else if (userChoice = `rock`) {
userChoice = 1}
else if (userChoice = `rock`) {
userChoice = 2}

//but that seems dreadfully inelegant

Answer 1

Here are 2 options to achieve what u want. (If I understood correctly)

let a = ["a1","a2", "a3"]

let input = "a2"

// option 1 (I don't know if you are allowed to use indexOf)
let input_to_number = a.indexOf(input)

console.log(input_to_number)

// option 2 (This is a little bit more elegant and generic than putting if else for every option)
let answear = -1
for(let i=0; i<a.length; i++){
    if(input === a[i]){
        answear = i
        break;
    }
}

console.log(answear)