javascript - Javascript为什么返回NaN？ [重复](Javascript why is it returns NaN? [duplicate])

Question

(This question already has answers here) :

((这个问题已经在这里有了答案)

：)

Sum numbers returns NaN (2 answers)

(总和数返回NaN （2个答案）)

Closed 15 hours ago .

(15小时前关闭。)

My code is:

(我的代码是：)

var inputtedCommand;
var input = document.getElementById("showInput");
document.addEventListener("keydown", function(e){
    console.log(e.which)
    console.log(e.key)

    var which = e.which
    var inputtedCommand = inputtedCommand + which;
    console.log(inputtedCommand)
    input.innerHTML = "- ", inputtedCommand;
});

And the inputtedCommand = NaN.

(并且inputtedCommand = NaN。)

How to make it to the pressed buttons?

(如何使其成为按下的按钮？)

  ask by I'm the man. translate from so

Answer 1

First you declare inputtedCommand as undefined:

(首先，您将inputtedCommand声明为undefined：)

var inputtedCommand;

then you try to add it to a number which will always return NaN

(那么您尝试将其添加到将始终返回NaN的数字中)

var inputtedCommand = inputtedCommand + which;

So change it to:

(因此将其更改为：)

var inputtedCommand = 0;
var input = document.getElementById("showInput");
document.addEventListener("keydown", function(e){
    console.log(e.which)
    console.log(e.key)

    var which = e.which
    var inputtedCommand = inputtedCommand + which;
    console.log(inputtedCommand)
    input.innerHTML = "- ", inputtedCommand;
});

and it won't blow up.

(它不会炸毁。)