如何让程序检查所选单词中是否有按键

我正在开发一款刽子手游戏，我正在检查用户通过按下键猜测的字母是否在随机选择的短语中。但无论信是否真的在俗语中，它要么总是给我"是的，它在俗语中"，要么"不是的，它不在谚语中"的答案。非常感谢您的帮助。谢谢。

这是我目前正在使用的代码。

document.addEventListener("keydown", function textFunction(event)
{
if (event.keyCode > 64 && event.keyCode < 91) 
{
    var guess = event.keyCode;
    var a = "a";
    var letterGuess = String.fromCharCode(event.keyCode);
    if(sayings[randomSaying].contains(guess)){
        alert("yes");
    } else {
        alert("no");
    }
    alert(String.fromCharCode(event.keyCode));
} 
else 
{
    alert("Please type a letter");
}
});

随机选择的

var sayings = [
    "cash on the nail",
    "charley horse",
    "double cross",
    "fit as a fiddle",
    "hands down",
    "if the cap fits",
    "mumbo jumbo",
    "see red",
    "stone the crows",
    "thick and thin",
]
sayings.toString();
var randomSaying = Math.floor(Math.random()*sayings.length);