本文探讨了在JavaScript中使用var声明变量的行为特征，包括其永久性特点、删除尝试时产生的错误、未声明变量的读取错误以及隐式全局变量的创建等问题。文章强调了在函数体内始终使用var声明变量的重要性。
[size=medium]Variables declared with var are permanent : attempting to delete them with the delete operator causes
an error.
If you attempt to read the value of an undeclared variable, JavaScript generates an error. If you assign a
value to a variable that you have not declared with var , JavaScript implicitly declares that variable for
you. Note, however, that implicitly declared variables are always created as global variables, even if they
are used within the body of a function. To prevent the creation of a global variable (or the use of an
existing global variable) when you meant to create a local variable to use within a single function, you
must always use the var statement within function bodies. It's best to use var for all variables, whether
global or local.[/size]
an error.
If you attempt to read the value of an undeclared variable, JavaScript generates an error. If you assign a
value to a variable that you have not declared with var , JavaScript implicitly declares that variable for
you. Note, however, that implicitly declared variables are always created as global variables, even if they
are used within the body of a function. To prevent the creation of a global variable (or the use of an
existing global variable) when you meant to create a local variable to use within a single function, you
must always use the var statement within function bodies. It's best to use var for all variables, whether
global or local.[/size]
扫一扫
764
被折叠的 条评论
为什么被折叠?
到【灌水乐园】发言
