Chrome开发者控制台输出未定义 [英] Chrome dev console outputting undefined

问题描述

每次我在网站上看到一些javascript代码时，我都想在Chrome开发人员的工具控制台上键入并试用它，而不是创建一个javascript文件，然后在浏览器中单独打开它.

Every time i see some javascript code on a website, I feel like typing and trying it out on the Chrome's developer's tool console instead of creating a javascript file and then opening it separately in the browser.

就像今天一样，我正在查看道格·克罗克福德(Doug Crockford)的Js演讲，并同时对他所说的要交叉检查该功能的内容进行测试.

Like today, I was viewing Doug Crockford's Js lecture and kept simultaneously running test on whatever he was saying to cross check that feature.

我在javascript控制台中注意到的一件奇怪的事情是，由于我执行的任何语句都不会产生固定值，因此它始终输出未定义的值，如下所示:

A strange thing that I noticed in the javascript console is that it always outputs the value undefined as a result of any statement that I execute that does not produce a fixed value as below:

var x = 12;控制台o/p<未定义

var x = 12; Console o/p < undefined

2 + 3控制台o/p<5

2+3 Console o/p < 5

+"46"<46

+"46" < 46

未定义的值表示每次声明后哪个Chrome开发者控制台.

What does the undefined value mean which Chrome dev console after every declaration.

推荐答案

如果键入时不带"var"，则只需

If you type it without "var", just

x = 12;

它将输出12;但无论如何，这是一个重复的问题: Chrome/Firefox console.log始终添加一行，表示未定义和这是什么意思，如果console.log(4)在Chrome控制台中未定义输出?

it will output 12; but in any case, this is a duplicate question of: Chrome/Firefox console.log always appends a line saying undefined and What does it mean if console.log(4) outputs undefined in Chrome Console?

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