javascript - 破坏 JavaScript 代码的特殊字符

Question

我正在为机械网站制作 JavaScript 闪卡游戏。因为我想将方程写在卡片上，所以我需要使用 delta(Δ) 符号。

一张卡片可能有:一侧是“功率方程”，另一侧是“P=W/Δt”。如果卡片从第一面开始，当按下空格键或按下翻转按钮时，它将翻转。但是，如果它从第二侧(带有 Δ 符号的一侧)开始，则按下“翻转”按钮或空格键时它不会翻转。

我尝试过不同的写法:

Δ Δ Δ

这些都不起作用。我的代码是:

//Copyright Attribution-ShareAlike 4.0 International 2017 Hazel Meehan


//array containing all options
var options = [ //counts from 0
  "Joules(J)", "Measure of Work",
  "Watts(W)", "Measure of Power",
  "Ek", "Kinetic Energy",
  "Ep", "Potential Energy",
  "Newtons(N)", "Measure of Force",
  "Pascals(Pa)", "Pressure",
  "ms-1", "Metres per Second",
  "ms-2", "Metres per Second Gained",
  "10N", "Value of Gravity",
  "Weight is a", "Force beginning with W",
  "The capacity to do work", "Energy is",
  "d = ΔvΔt is the equation for", "The equation for distance",
  "W=FΔd is the equation for", "The equation for work",
  "P=W/Δt is the equation for", "The equation for power"
];

//initialize variables
var randomNum = 0;
var sideOne = " ";
var sideTwo = " ";

//choose new card using random number
var newCard = function() { //runs on 'next'
  var randomNum = Math.floor(Math.random() * options.length);
  sideOne = options[randomNum];
  if (randomNum % 2 == 0) { //is the number even
    sideTwo = options[randomNum + 1];
  } else {
    sideTwo = options[randomNum - 1];
  }
  document.getElementById("card").innerHTML = sideOne;
};

//show other side of card
var flip = function() { //runs on 'flip'
  if (document.getElementById("card").innerHTML == sideOne) {
    document.getElementById("card").innerHTML = sideTwo;
  } else {
    document.getElementById("card").innerHTML = sideOne;
  }
};

//change card on key down
document.onkeydown = function(e) {
  e = e || window.event;
  if (e.keyCode == '39') { //right arow key
    newCard();
  } else if (e.keyCode == '32') { //space bar
    flip();
  }
}

<article>
  <h2>Flashcards</h2>
  <center><button id="flashButton" onclick="newCard()">Next</button></center>
  <br>
  <center><button id="card"></button></center>
  <br>
  <center><button id="flashButton" onclick="flip()">Flip</button></center>
</article>

Answer 1

检查元素的innerHtml(if (document.getElementById("card").innerHTML == sideOne))时，之前设置的字符串已被解释为html当检索它时，Δ 现在将是 Δ。那么比较结果是错误的:

"d = ΔvΔt 是"!== "d = ΔvΔt 是"的方程式

因此它再次将 innerHtml 设置到同一侧。