為什么我的變量在 javascript 中返回 undefined？
[英]Why is my variable returning undefined in javascript?
問題描述
我是 javascript 新手。 我正在制作一個抽認卡程序。 出於某種原因，盡管將變量 lastPress 定義為全局變量，但 lastPress 似乎返回 undefined。 但是，它不會導致 JSHint 中的錯誤。 這是我的代碼：
var i = 0; var questions = ["1: Was the human migration caused by an ice age?", "True"]; var answer = [true, true]; var lastPress; document.getElementById("question").innerHTML = questions[i]; function itsTrue() { lastPress = true; } function itsFalse() { lastPress = false; } function getAns() { if (answer[i] == lastPress) { document.getElementById("ans").innerHTML = "You're correct! The answer was " + lastPress; } else { document.getElementById("ans").innerHTML = "We're sorry, but that is not correct. You said " + lastPress + ". The answer was " + answer[i]; } i++; document.getElementById("question").innerHTML = questions[i]; } document.getElementById("true").onclick = function(){itsTrue()}; document.getElementById("true").onclick = function(){getAns()}; document.getElementById("false").onclick = function(){itsFalse()}; document.getElementById("false").onclick = function(){getAns()};
<!DOCTYPE HTML> <html> <head> <title>Flash cards</title> </head> <body> <p id="question">This is where the question shows up</p> <p id="ans">This is where the result will show up</p> <button type="button" id="true">True</button> <button type="button" id="false">False</button> </body> </html>
2 個解決方案
解決方案1
1 已采納 2019-12-09 20:38:55
如果您想為同一個點擊事件定義多個函數：此外，在第二次按下真假按鈕后，我將增加到 2，因此問題 [2] 未定義
var i = 0; var questions = ["1: Was the human migration caused by an ice age?", "True"]; var answer = [true, true]; var lastPress; document.getElementById("question").innerHTML = questions[i]; function itsTrue() { console.log('true') lastPress = true; } function itsFalse() { console.log('false'); lastPress = false; } function getAns() { if (answer[i] == lastPress) { document.getElementById("ans").innerHTML = "You're correct! The answer was " + lastPress; } else { document.getElementById("ans").innerHTML = "We're sorry, but that is not correct. You said " + lastPress + ". The answer was " + answer[i]; } i++; console.log(i); document.getElementById("question").innerHTML = questions[i]; } document.getElementById("true").onclick = function(){itsTrue();getAns();}; //document.getElementById("true").onclick = function(){getAns()}; document.getElementById("false").onclick = function(){itsFalse(),getAns();}; // document.getElementById("false").onclick = function(){getAns()};
<!DOCTYPE HTML> <html> <head> <title>Flash cards</title> </head> <body> <p id="question">This is where the question shows up</p> <p id="ans">This is where the result will show up</p> <button type="button" id="true">True</button> <button type="button" id="false">False</button> </body> </html>
解決方案2
0 2019-12-09 20:25:43
在您的問題中，不清楚返回 undefined 的內容，所以我認為它是您的 HTML 中更新的內容。
您的代碼返回 undefined 因為您每次點擊都會增加i 。 但是你的數組只有兩個元素長。 您需要處理所有問題都已顯示的事實。 在這里，我只是將變量i重置為 0，但我不確定這是否適用於您的情況。
var i = 0; var questions = ["1: Was the human migration caused by an ice age?", "2. this is a second question, true or false ? ", "3. did i got you with my last tricky question?"]; var answer = [true, true, false]; var lastPress; document.getElementById("question").innerHTML = questions[i]; function itsTrue() { lastPress = true; } function itsFalse() { lastPress = false; } function getAns() { if (answer[i] == lastPress) { document.getElementById("ans").innerHTML = "You're correct! The answer was " + lastPress; } else { document.getElementById("ans").innerHTML = "We're sorry, but that is not correct. You said " + lastPress + ". The answer was " + answer[i]; } i++; if(i >= questions.length) { i = 0; } document.getElementById("question").innerHTML = questions[i]; } document.getElementById("true").onclick = function(){itsTrue(); getAns() }; document.getElementById("false").onclick = function(){itsFalse(); getAns()};
<!DOCTYPE HTML> <html> <head> <title>Flash cards</title> </head> <body> <p id="question">This is where the question shows up</p> <p id="ans">This is where the result will show up</p> <button type="button" id="true">True</button> <button type="button" id="false">False</button> </body> </html>
為什么我的變量表數據返回未定義？
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