问题描述
每次执行 console.log 时，都会在输出日志中附加一行 undefined.
Every time console.log is executed, a line saying undefined is appended to the output log.
它发生在 Windows 和 Linux 上的 Firefox 和 Chrome 中.
It happens in both Firefox and Chrome on Windows and Linux.
推荐答案
如果你从一个 JS 文件运行 console.log()，这个 undefined 行应该不附加.
If you're running console.log() from a JS file, this undefined line should not be appended.
如果您是从控制台本身运行 console.log()，那是有道理的.这就是原因:在控制台中，您可以键入变量的名称(例如，尝试键入 window)并打印有关它的信息.当您从控制台运行任何 void 函数(如 console.log)时，它还会打印出有关返回值的信息，在这种情况下为 undefined.
If you're running console.log() from the console itself, it makes sense. This is why: In the console you can type a name of a variable (for example try typing window) and it prints info about it. When you run any void function (like console.log) from the console, it also prints out info about the return value, undefined in this case.
我在我的 Chrome(Mac 版本 23.0.1271.101)上测试了这两种情况，当我在控制台中运行它时确实看到了 undefined 行.当我在控制台中写这行时，也会出现这个 undefined: var bla = "sdfdfs"
I tested both cases on my Chrome (Mac ver 23.0.1271.101) and indeed I see the undefined line when I run it inside the console. This undefined also appears when I write this line in the console: var bla = "sdfdfs"
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