[英]Do parentheses prevent semicolon insertion?
Say that I want to set a bunch of variables equal to null (and don't want to use an array/loop structure) or maybe I just want to write a large boolean expression across multiple lines. 假设我想设置一组等于null的变量(并且不想使用数组/循环结构)或者我只想在多行中编写一个大的布尔表达式。 Does an unclosed parenthetical prevent semicolon insertion in such a case?
在这种情况下,未公开的括号是否会阻止分号插入? Eg
例如
some_variable = another_variable = yet_another_variable = (
oh_look_a_parenthesis_above_me = hey_heres_another_variable) = (
and_for_some_reason_another = last_one) = null;
Or 要么
if(test_for_some_complex_expr && another_test || (
but_maybe_this_one && or_this_one)) {
// ...
}
And how does this compare versus using &&
or ||
这与使用
&&
或||
相比如何进行比较 or =
to group expressions over line breaks? 或
=
在换行符上分组表达式? Ie, would this always work too? 即,这总是有效吗?
some_variable = another_variable =
a_variable_after_a_line_break = and_one_more;
while(test_for_an_expr && another_test ||
(an_expr_here && and_an_expr_here)) {
// ...
}
I'm looking for the way that is most standard across all browsers (including IE6+). 我正在寻找所有浏览器(包括IE6 +)最标准的方式。
Semicolon insertion only happens if you have code which would be a syntax error without the semicolon. 如果你的代码是没有分号的语法错误,则只会发生分号插入。 In your case the expression is perfectly valid, so you don't need to worry about semicolon insertion - parentheses or not.
在您的情况下,表达式是完全有效的,因此您不必担心分号插入 - 括号或不括号。
An example where semicolon insertion will happen: 以分号插入的示例:
var a = 1
var b = 2
In the above case, a semicolon is inserted at the line break, but only because it is a syntax error to write: 在上面的例子中,在换行符处插入分号,但这只是因为写入语法错误:
var a = 1 var b = 2
but it is perfectly valid to write: 但写完是完全有效的:
var a = 1; var b = 2
The rules get tricky because there are some instances in JavaScript syntax where line breaks are NOT allowed. 规则变得棘手,因为JavaScript语法中存在一些不允许换行的实例。 For example a line break is NOT allowed between the '
return
' keyword and a value to return. 例如,'
return
'关键字和要返回的值之间不允许换行。 So this is a syntax error: 所以这是一个语法错误:
return
17;
But the way semicolon insertion "fixes" this error is by inserting a semicolon like this: 但分号插入“修复”此错误的方式是插入一个像这样的分号:
return;
17;
Which is probably not what the writer intended! 这可能不是作家的意图! In that particular case, a parenthesis can be used to prevent semicolon insertion:
在该特定情况下,可以使用括号来防止分号插入:
return (
17);
Because it only between the return keyword and the start of the expression that line break is disallowed. 因为它只在return关键字和表达式的开头之间不允许换行。 Inside an expression it is not a problem.
在表达式中,这不是问题。
Does an unclosed parenthetical prevent semicolon insertion in such a case?
在这种情况下,未公开的括号是否会阻止分号插入?
Yes. 是。 Although it is unnecessary:
虽然没必要:
And how does this compare versus using
&&
or||
这与使用
&&
或||
相比如何进行比较 or=
to group expressions over line breaks?或
=
在换行符上分组表达式?
It's exactly the same. 它完全一样。 They are expressions that require a second part, therefore ASI cannot - must not - kick in without making the result invalid.
它们是需要第二部分的表达式,因此ASI不能 - 不得 - 在不使结果无效的情况下启动。
ASI will only occur when the continued line is invalid without the semicolon. 只有在没有分号的情况下连续行无效时才会发生ASI。 See What are the rules for JavaScript's automatic semicolon insertion (ASI)?
请参阅JavaScript的自动分号插入(ASI)的规则是什么? for details.
详情。
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.