我试图用输入增加和减少数字来制作一个简单有趣的系统，但它不起作用

Question

I tried the script and its working well for the first 2 functions, but then when I added the third one, the entire page just doesn't work. Can I know why and how to fix?

I am a beginner Javascripter and I still need practices so can you guys explain someway suitable for my level?

 let a = 0, b = 1 function inc() { a += b document.getElementById("x").innerHTML = "x" + " " + "=" + " " + a; }; function dec() { a -= b document.getElementById("x").innerHTML = "x" + " " + "=" + " " + a; }; function input() { if (document.getElementById("input").innerHTML == null) { } else { b = Number(document.getElementById("input").innerHTML); }; };

 body { background-color: powderblue; }

 <h1>Online simple Javascript project!</h1> <p id="x">x = 0</p><!-- Result --> <p><br><br>Change the power here!</p><!-- // Description --> <input id="input"><button type="button" onclick="input()">Apply</button><!-- // Button that save your power --> <h2>Click the button to increase x</h2><!-- // Description --> <button type="button" onclick="inc()">Increase</button><!-- // Increase --> <h2>Click the button to decrease x</h2><!-- // Description --> <button type="button" onclick="dec()">Decrease</button><!-- // Decrease -->

Answer 1

Use value instead of innerHTML for input

function input() {
  if (document.getElementById("input").value != null){
    b = Number(document.getElementById("input").value);
  };
};