[英]Why are global and this.something variables not decleared?
When I used a new variable something.something or this.something, my code worked when I omitted the var keyword: 当我使用一个新变量something.something或this.something时,我的代码在省略var关键字时起作用:
this.something = 1;
something.something = 1;
but when I write 但是当我写作
var this.something = 1;
var something.something = 1;
it doesn't work. 它不起作用。
Why? 为什么?
I suppose because var
expects a valid identifier, and .
我想因为
var
需要一个有效的标识符,并且.
is not a valid character for an identifier. 不是标识符的有效字符。
It thinks you want the variable name to actually be this.something
, which isn't valid. 它认为您希望变量名实际上是
this.something
,这是无效的。
When testing the two versions, I get slightly different errors. 在测试这两个版本时,我会遇到稍微不同的错误。
The one with this.something
tells me: 有这个
this.something
告诉我:
SyntaxError: Unexpected token this
SyntaxError:意外的令牌
The one with something.something
tells me: 带有
something.something
那个something.something
告诉我:
SyntaxError: Unexpected token .
SyntaxError:意外的令牌。
Same error, but the invalid token in the first is the keyword this
. 同样的错误,但第一个中的无效令牌是关键字
this
。
You can't declare a this
field (member field), or a field of another object. 您不能声明
this
字段(成员字段)或另一个对象的字段。 It's simply not valid syntax. 这根本就不是有效的语法。
You use var
to declare local variables, which are either function-level or (if you're not in a function) global. 您可以使用
var
来声明局部变量,这些变量可以是函数级的,也可以是(如果您不在函数中)全局变量。 And as Patrick said, a variable name can not contain a period. 正如帕特里克所说,变量名称不能包含句点。
var
is the syntax for declaring a variable. var
是声明变量的语法。 In Javascript simply by assigning a value to a property it will attach the property to the object. 在Javascript中,只需为属性赋值,它就会将属性附加到对象。
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