我无法弄清楚为什么我不能在三元运算中使用我的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;
}
};
具体来说 case where m == 'voice' and typeof == 'object' 会抛出错误"Uncaught SyntaxError: Unexpected token for" . 如果我改变那个案例是:
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;
......然后一切都按预期工作 .
为什么是这样??
2 回答
三元运算符的语法要求"branches"是表达式 . 你不能只在那里任意陈述;在JavaScript中,
for
循环不是表达式 .你可以将循环包装在函数中并调用它,但是使用普通的
if
语句会简单得多 .如果你将for循环包装在括号中它可能会起作用 .
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Conditional_Operator
但风格上你真的在推动信封......