我知道在 Javascript 中的所有语句之后使用分号是一种很好的语法,但是有人知道为什么 if/else 语句在大括号之后不需要它们吗?
{
and }
begin and close a group of statements Basically, an if-else
must be followed by either a statement or a group of statements.
if-else
followed by a statement:
if (condition) statement;
if (condition); // followed by a statement (an empty statement)
if-else
followed by group of statements:
if (condition) {
statement;
statement;
}
if (condition) {
// followed by a group of statements of zero length
}
if-else
must end with a ;
if it is followed by a single statement. if-else
does not end with a ;
when followed by a group of statements because ;
is used to end a single statement, and is not used for ending a group of statements.
The real answer is because many modern languages copied their syntax from C, which has this property. JavaScript is one of these languages.
C allows statement blocks
{ ... }
(which don't need terminating semicolons) to be used where statements can be used. So you can use statement blocks as then- and else- clauses, without the semicolons.
If you place a single statement in the then- or else- clause, you'll need to terminate it with a semicolon. Again, just as in C, with the extra JavaScript twist that ; is optional at the end of a line, if inserting it would not cause a syntax error.
Because the curly braces themselves are termination characters.
They are tokens that enclose a compound statement block and are intrinsically terminated. It's like putting a period at the end of a sentence, it signals to the parser that the thought is complete.
While being completely ugly it is valid to wrap every statement in {} and omit the ;
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