From 33058f2b292b3a581333bdfb21b8f671898c5060 Mon Sep 17 00:00:00 2001 From: Peter Bengtsson Date: Tue, 8 Dec 2020 14:40:17 -0500 Subject: initial commit --- .../errors/redeclared_parameter/index.html | 62 ++++++++++++++++++++++ 1 file changed, 62 insertions(+) create mode 100644 files/zh-cn/web/javascript/reference/errors/redeclared_parameter/index.html (limited to 'files/zh-cn/web/javascript/reference/errors/redeclared_parameter') diff --git a/files/zh-cn/web/javascript/reference/errors/redeclared_parameter/index.html b/files/zh-cn/web/javascript/reference/errors/redeclared_parameter/index.html new file mode 100644 index 0000000000..9a53795180 --- /dev/null +++ b/files/zh-cn/web/javascript/reference/errors/redeclared_parameter/index.html @@ -0,0 +1,62 @@ +--- +title: 'SyntaxError: redeclaration of formal parameter "x"' +slug: Web/JavaScript/Reference/Errors/Redeclared_parameter +tags: + - Errors + - JavaScript + - SyntaxError +translation_of: Web/JavaScript/Reference/Errors/Redeclared_parameter +--- +
{{jsSidebar("Errors")}}
+ +

信息

+ +
SyntaxError: redeclaration of formal parameter "x" (Firefox)
+SyntaxError: Identifier "x" has already been declared (Chrome)
+SyntaxError: Cannot declare a let variable twice: 'x' (WebKit)
+
+ +

错误类型

+ +

{{jsxref("SyntaxError")}}

+ +

哪里出错了?

+ +

某个变量名称已经作为函数参数出现了,但是又使用了 let 在函数体里重声明了。在JavaScript 中不允许使用let在相同的函数或块范围内重新声明相同的变量。

+ +

示例

+ +

在本例中,参数 "arg" 又重新声明了:

+ +
function f(arg) {
+  let arg = "foo";
+}
+
+// SyntaxError: redeclaration of formal parameter "arg"
+
+ +

如果要更改函数体中的“arg”的值,可以像下面一样,但不需要再次声明同一个变量。 换句话说:你可以省略 let 关键字。 如果要创建一个新变量,则需要将其重命名,因为其与函数参数有冲突。

+ +
function f(arg) {
+  arg = "foo";
+}
+
+function f(arg) {
+  let bar = "foo";
+}
+
+ +

兼容性提醒

+ + + +

相关

+ + -- cgit v1.2.3-54-g00ecf