從Javascript中退出函數。簡單的搖滾，紙，剪刀遊戲

Question

如果userChoice爲空或除岩石，紙張或剪刀之外的單詞，我該如何停止執行此功能。 我試圖使用返回，但我無法讓它工作。 任何幫助表示讚賞。 感謝

JS小提琴鏈接= http://jsfiddle.net/Renay/d9bea2ra/1/

var userChoice = prompt('Do you choose rock, paper or scissors?'); 
var compChoice = Math.random(); 

if (compChoice <= 0.34) { 
    compChoice = 'rock'; 
} else if (compChoice <= 0.67) { 
    compChoice = 'paper'; 
} else { 
    compChoice = 'scissors'; 
} 

function compare() { 
    if (userChoice == compChoice) { 
     console.log('The result is a tie!'); 
    } else if ((userChoice == 'rock' && compChoice == 'scissors') || (userChoice == 'paper' && compChoice == 'rock') || (userChoice == 'scissors' && compChoice == 'paper')) { 
     console.log('You win!'); 
    } else { 
     console.log('You lose!'); 
    } 

    if (userChoice === null) { 
     console.log('Please select an option');  
    } else if (userChoice !== 'rock'&&'paper'&&'scissors') { 
     console.log('Please select rock, paper or scissors');  
    } 
} 

console.log('Your choice = ' + userChoice); 
console.log('Computer Choice = ' + compChoice); 
compare(); 

Answer 1

您的if語句中的條件是錯誤的。它應該是：

if (userChoice !== 'rock' && userChoice !== 'paper' && userChoice !== 'scissors') 

形式e1 && e2 && e3 && ...的表達式計算，如果所有的人都truthy持續eN子表達式。所以，你的測試是等價於：

if (userChoice !== 'scissors') 

你應該把那張支票之前顯示遊戲的結果，並從函數返回即可。所以它應該是：

function compare() { 
    if (userChoice === null) { 
     console.log('Please select an option');  
     return; 
    } else if (userChoice !== 'rock' && userChoice !== 'paper' && userChoice !== 'scissors') { 
     console.log('Please select rock, paper or scissors'); 
     return; 
    } 

    if (userChoice == compChoice) { 
     console.log('The result is a tie!'); 
    } else if ((userChoice == 'rock' && compChoice == 'scissors') || (userChoice == 'paper' && compChoice == 'rock') || (userChoice == 'scissors' && compChoice == 'paper')) { 
     console.log('You win!'); 
    } else { 
     console.log('You lose!'); 
    } 

} 

Answer 2

只是做return;

function compare() { 
    if(!userChoice) 
    return; 
    // (...) more code 
} 

一個return調用退出函數。但請注意，您只能在function內使用return

Answer 3

如果我理解正確，您想返回到代碼的開頭。你應該換行整個事情的功能，然後再調用該函數：

function rockPaperScissors() { 
    var userChoice = prompt('Do you choose rock, paper or scissors?'); 
    var compChoice = Math.random(); 

    if (compChoice <= 0.34) { 
     compChoice = 'rock'; 
    } else if (compChoice <= 0.67) { 
     compChoice = 'paper'; 
    } else { 
     compChoice = 'scissors'; 
    } 

    function compare() { 
     if (userChoice == compChoice) { 
      console.log('The result is a tie!'); 
     } else if ((userChoice == 'rock' && compChoice == 'scissors') || (userChoice == 'paper' && compChoice == 'rock') || (userChoice == 'scissors' && compChoice == 'paper')) { 
      console.log('You win!'); 
     } else { 
      console.log('You lose!'); 
     } 

     if (userChoice === null) { 
      console.log('Please select an option'); 
      rockPaperScissors(); 
     } else if (userChoice !== 'rock' && userChoice !== 'paper' && userChoice !== 'scissors') { // fixed 
      console.log('Please select rock, paper or scissors'); 
      rockPaperScissors(); 
     } 
    } 

    console.log('Your choice = ' + userChoice); 
    console.log('Computer Choice = ' + compChoice); 
    compare(); 
} 
rockPaperScissors(); 

您也有一個錯誤與檢查，如果它不是石頭，紙，或剪刀之一，所以我固定的。 （It seems Barmar got to it before me）

Answer 4

我更新了功能的每個的if/else部分退出時，它匹配的if/else條件與return false。另外，我將if (userChoice === null)檢查更改爲if (userChoice === "")，因爲它看起來像prompt('Do you choose rock, paper or scissors?');在用戶沒有輸入任何值時返回空字符串。 Fiddle此外，我剛剛更新了函數的開頭，以便根據** Barmar'的建議（他第一次正確使用它）。

function compare() { 
    if (userChoice === "") { 
     console.log('Please select an option'); 
     return false; 
    } else if ((userChoice !== 'rock') && (userChoice !=='paper') && (userChoice !=='scissors')) { 
     console.log('Please select rock, paper or scissors'); 
     return false; 
    } 

    if (userChoice == compChoice) { 
     console.log('The result is a tie!'); 
     return false; 
    } else if ((userChoice == 'rock' && compChoice == 'scissors') || (userChoice == 'paper' && compChoice == 'rock') || (userChoice == 'scissors' && compChoice == 'paper')) { 
     console.log('You win!'); 
     return false; 
    } else { 
     console.log('You lose!'); 
     return false; 
    } 
}