在函数字符串上使用eval [英] Using eval on a function string

问题描述

我正在做：

eval('function(){ console.log("Hello World"); }')();

但这会产生错误：

Uncaught SyntaxError: Unexpected token (

为什么这是错的？

推荐答案

eval 运算符需要程序为输入和JavaScript的语法要求所有
顶级程序元素都是声明或语句。

The eval operator expects a Program as input, and the grammar of JavaScript requires that all top-level program elements are either declarations or statements.

规范说：

让编程是ECMAScript代码，它是将x解析为程序的结果。

Let prog be the ECMAScript code that is the result of parsing x as a Program.

function 无法启动顶级语句，但它可以启动一个函数声明，但只有当它有一个名字。

function can't start a top-level statement, but it can start a function declaration, but only when it has a name.

这就是你得到意外的令牌的原因（;它需要在括号之前打开参数列表的函数名。

That's why you get "Unexpected token ("; it expects a function name before the parenthesis that opens the argument list.

正如其他人所说， eval 很有趣ction，你需要欺骗JavaScript解析器找到一个需要语句的表达式。用括号包裹身体是一种方法。

As others have noted, to eval a function, you need to trick the JavaScript parser into finding an expression where it expects a statement. Wrapping the body in parentheses is one way to do this.

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