问题描述
当我尝试使用 var 定义变量时，一切正常.
When I try to define a variable using var, everything is working.
但是将其定义为 const 并没有按预期工作，并且变量未定义.
But defining it as const is not working as expected and the variable is undefined.
window.eval("var v = 5;");
document.body.innerHTML += window.v === undefined;
window.eval("const l = 5;");
document.body.innerHTML += window.l === undefined;我已经在 Chrome 和 Node.js 上对其进行了测试.我错过了什么吗?
I have tested it on Chrome and Node.js. Am I missing something?
提前谢谢你！
推荐答案
在 eval 代码中使用 let 和 const 不会调用 strict模式.let 和 const 是 lexicalDeclarations，将它们的范围限制在封闭的词法范围内.
Using let and const in eval code doesn't invoke strict mode. let and const are lexicalDeclarations, which limits their scope to the enclosing lexical scope.
词法作用域由块和直接调用 eval 创建(参见 运行时语义:PerformEva 步骤 12).
A lexical scope is created by a block and by direct call to eval (see Runtime Semantics: PerformEva step 12).
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