javascript不會在for之后執行代碼

Question

我在javascript中創建了2個函數，這些函數會在click事件上觸發，問題是for循環后，警報沒有執行。

 function myfunc() { for (var i = 0; i < 4; i++) { document.getElementsByTagName("h1")[i].style.color="red"; } alert("alert 1"); //this should be executed after the for since it is part of the function code. } function myfunc2() { for (var j = 0; j < 4; j++) { document.getElementsByTagName("h1")[j].style.color="navy"; } alert("alert 2"); //this should be executed after the for since it is part of the function code } 

 <h1 onClick="myfunc()">primo h1</h1> <h1 onClick="myfunc2();">secondo h1</h1> 

Answer 1

應用新的樣式屬性之前，您需要檢查DOM中有多少個h1標簽。 您實際上是在嘗試對undefined進行更改。

 var elements = document.getElementsByTagName("h1"); function myfunc() { for (var i = 0; i < elements.length; i++) { elements[i].style.color="red"; } alert("alert 1"); //this should be executed after the for since it is part of the function code. } function myfunc2() { for (var j = 0; j < elements.length; j++) { elements[j].style.color="navy"; } alert("alert 2"); //this should be executed after the for since it is part of the function code } 

 <h1 onClick="myfunc()">primo h1</h1> <h1 onClick="myfunc2();">secondo h1</h1>