javascript - javascript中的递归函数未定义

Question

我花了大约一个小时试图弄清楚为什么我从这个函数中得到未定义的结果，该函数运行良好，当条件触发并且randomAlphabet的值正确时它会停止，当然是一个愚蠢的错误，但它让我觉得很烦人。 这是代码:

(function() {

  var getAlphabet = function() {
    var alphabet = [];
    for ( var asciiCode = 97; asciiCode < 123; asciiCode++ ) {
      alphabet.push(String.fromCharCode(asciiCode));
    }
    return alphabet;
  };

  var getRandomAlphabet = function(alphabet, randomAlphabet) {

    var alphabet = alphabet || getAlphabet();
    var alphabetLength = alphabet.length;
    var randomAlphabet = randomAlphabet || [];

    if ( alphabetLength === 0 ) {
      return randomAlphabet;
    };

    var getRandomIndex = function(min, max) {
      return Math.floor(Math.random() * (max - min) + min);
    };

    // remove the random item from the original alphabet
    var randomIndex = getRandomIndex(0, alphabetLength);
    var randomItem = alphabet.splice(randomIndex, 1)[0]; 

    // add the random item to the random alphabet
    randomAlphabet = randomAlphabet.concat(randomItem);

    getRandomAlphabet(alphabet, randomAlphabet);

  };

  // this returns undefined
  console.log(getRandomAlphabet()); 

})();

Answer 1

唯一的事情是你需要返回getRandomAlphabet方法

(function() {

  var getAlphabet = function() {
    var alphabet = [];
    for ( var asciiCode = 97; asciiCode < 123; asciiCode++ ) {
      alphabet.push(String.fromCharCode(asciiCode));
    }
    return alphabet;
  };

  var getRandomAlphabet = function(alphabet, randomAlphabet) {

    var alphabet = alphabet || getAlphabet();
    var alphabetLength = alphabet.length;
    var randomAlphabet = randomAlphabet || [];

    if ( alphabetLength === 0 ) {
      return randomAlphabet;
    };

    var getRandomIndex = function(min, max) {
      return Math.floor(Math.random() * (max - min) + min);
    };

    // remove the random item from the original alphabet
    var randomIndex = getRandomIndex(0, alphabetLength);
    var randomItem = alphabet.splice(randomIndex, 1)[0]; 

    // add the random item to the random alphabet
    randomAlphabet = randomAlphabet.concat(randomItem);

    return getRandomAlphabet(alphabet, randomAlphabet);

  };

  // this returns undefined
  console.log(getRandomAlphabet()); 

})();