Javascript ternary w/ for loop error; "Uncaught SyntaxError: Unexpected token for"

Question

我不明白为什么我不能在三元运算中使用 for 循环。这是不起作用的代码：

this.ask = function() {
  m = (isVoice) ? 'voice' : 'text';
  switch (true) {
    case m == 'voice' && typeof questions[timer.question].voice == 'string':
      (++timer.attempts > timer.maxAttempts) ?
        console.log('Stop'):
        console.log('Play file (' + timer.attempts + '): ' + questions[timer.question].voice);
      break;
    case m == 'voice' && typeof questions[timer.question].voice == 'object':
      (++timer.attempts > timer.maxAttempts) ?
        console.log('Stop'):
        for (i = 0; i < questions[timer.question].voice.length; i++) {
          console.log(questions[timer.question].voice[i])
        };
      break;
    default:
      (++timer.attempts > timer.maxAttempts) ?
        console.log('Stop'):
        console.log('Say Text (' + timer.attempts + '): ' + questions[timer.question].text);
      break;
  }
};

特别是 m == 'voice' 和 typeof == 'object' 的情况抛出错误 "Uncaught SyntaxError: Unexpected token for"。如果我将那个案例更改为：

case m == 'voice' && typeof questions[timer.question].voice == 'object':
            console.log('Audio, Array.');
            if (++timer.attempts > timer.maxAttempts) {
                console.log('Stop');
            }
            else {
                for (i in questions[timer.question].voice) {
                    console.log(questions[timer.question].voice[i]);
                }
            }
            break;

...然后一切正常。

这是为什么？

Answer 1

三元运算符的语法要求 "branches" 是表达式。您不能只是在那里放置任何任意语句；在 JavaScript 中，for 循环不是表达式。

您可以将循环包装在一个函数中并调用它，但只使用普通的 if 语句会简单得多。

Answer 2

如果将 for 循环括在括号中，它可能会起作用。

function() {
    for (i = 0; i < questions[timer.question].voice.length; i++) {
     console.log(questions[timer.question].voice[i])
    }
}()

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Conditional_Operator

但从风格上讲，您确实在挑战极限...

Javascript ternary w/ for loop error; "Uncaught SyntaxError: Unexpected token for"

Javascript ternary w/ for loop error; "Uncaught SyntaxError: Unexpected token for"

javascript

for-loop

ternary