看不懂，求大神們來詳細(xì)解答一下，任務(wù)1,2,3的步驟
<html>
??? <head>
??????? <meta http-equiv="Content-Type" content="text/html; charset=gb2312">
??????? <title>無標(biāo)題文檔</title>
??? </head>
?? ?
??? <body>
??????? <form>
????????? 請選擇你愛好:<br>
????????? <input type="checkbox" name="hobby" id="hobby1">? 音樂
????????? <input type="checkbox" name="hobby" id="hobby2">? 登山
????????? <input type="checkbox" name="hobby" id="hobby3">? 游泳
????????? <input type="checkbox" name="hobby" id="hobby4">? 閱讀
????????? <input type="checkbox" name="hobby" id="hobby5">? 打球
????????? <input type="checkbox" name="hobby" id="hobby6">? 跑步 <br>
????????? <input type="button" value = "全選" onclick = "checkall();">
????????? <input type="button" value = "全不選" onclick = "clearall();">
????????? <p>請輸入您要選擇愛好的序號，序號為1-6:</p>
????????? <input id="wb" name="wb" type="text" >
????????? <input name="ok" type="button" value="確定" onclick = "checkone();">
??????? </form>
?????? ?
?????? ?
?????? ?
?????? ?
?????? ?
?????? ?
?????? ?
??????? <script type="text/javascript">
??????? function checkall(){
??????????? var hobby = document.getElementsByTagName("input");
????????? ?
????????? // 任務(wù)1
?????????? for(var i=0;i<hobby.length;i++){
?????????????? hobby[i].checked=true
?????????? }
??????? }
??????? function clearall(){
??????????? var hobby = document.getElementsByName("hobby");
?????????????? for(var i=0;i<hobby.length;i++){
?????????????? hobby[i].checked=false
?????????? }
???????? // 任務(wù)2?? ?
?????????? ?
??????? }
?????? ?
??????? function checkone(){
??????????? var j=document.getElementById("wb").value;
??????????? if(parseInt(j)>6||parseInt(j)<1){
??????????????? alert("請重新輸入")
??????????? }
??????? document.getElementById("hobby"+j).checked = true;
???????? // 任務(wù)3
?????? ?
??????? }
?????? ?
??????? </script>
2016-08-05
<html>
??? <head>
??????? <meta http-equiv="Content-Type" content="text/html; charset=gb2312">
??????? <title>無標(biāo)題文檔</title>
??? </head>
?? ?
??? <body>
??????? <form>
????????? 請選擇你愛好:<br>
????????? <input type="checkbox" name="hobby" id="hobby1">? 音樂
????????? <input type="checkbox" name="hobby" id="hobby2">? 登山
????????? <input type="checkbox" name="hobby" id="hobby3">? 游泳
????????? <input type="checkbox" name="hobby" id="hobby4">? 閱讀
????????? <input type="checkbox" name="hobby" id="hobby5">? 打球
????????? <input type="checkbox" name="hobby" id="hobby6">? 跑步 <br>
????????? <input type="button" value = "全選" onclick = "checkall();">
????????? <input type="button" value = "全不選" onclick = "clearall();">
????????? <p>請輸入您要選擇愛好的序號，序號為1-6:</p>
????????? <input id="wb" name="wb" type="text" >
????????? <input name="ok" type="button" value="確定" onclick = "checkone();">
??????? </form>
?????? ?
?????? ?
??????? <script type="text/javascript">
??????? function checkall(){
??????????? var hobby = document.getElementsByTagName("input"); ? ? //尋找文檔中input標(biāo)簽，并將input標(biāo)簽按順序賦值給hobby，所以此時hobby包含的是個數(shù)組
????????? // 任務(wù)1?
?????????? for(var i=0;i<hobby.length;i++){
?????????????? hobby[i].checked=true
?????????? } //定義一個for循環(huán)函數(shù)循環(huán)次數(shù)為hobby數(shù)組的長度，每執(zhí)行一次循環(huán)即給hobby數(shù)組其中的第（i）個元素的chenked屬性賦一個“true”值。
??????? }
??????? function clearall(){
??????????? var hobby = document.getElementsByName("hobby");
?????????????? for(var i=0;i<hobby.length;i++){
?????????????? hobby[i].checked=false
?????????? }//恕我有點懶，同上，賦值false。
???????? // 任務(wù)2?? ?
?????????? ?
??????? }
?????? ?
??????? function checkone(){
??????????? var j=document.getElementById("wb").value;//將id為wb的元素的值賦給j。
??????????? if(parseInt(j)>6||parseInt(j)<1){
??????????????? alert("請重新輸入")
??????????? }//當(dāng)給j賦予的值大于6，當(dāng)給j賦予的值小于1時。彈出提示框——請重新輸入。? ? ? ? document.getElementById("hobby"+j).checked = true;
//否則給hobby數(shù)組其中的第（j）個元素的chenked屬性賦一個“true”值。
???????? // 任務(wù)3
?????? ?
??????? }
?????? ?
??????? </script>
2016-08-03
? ? ?function checkall(){
??????????? var hobby = document.getElementsByTagName("input"); ?//得到關(guān)于對象input的數(shù)組(就是根據(jù)name得到六個選擇)
????????? ?
????????? // 任務(wù)1?
?????????? for(var i=0;i<hobby.length;i++){ ?
?????????????? hobby[i].checked=true ?//轉(zhuǎn)換過來意思是，六個選擇逐一打勾
?????????? }
??????? }
??????? function clearall(){
??????????? var hobby = document.getElementsByName("hobby"); ?////得到關(guān)于對象input的數(shù)組(就是根據(jù)name得到六個選擇)
?????????????? for(var i=0;i<hobby.length;i++){
?????????????? hobby[i].checked=false ?////轉(zhuǎn)換過來意思是，六個選擇逐一取消打鉤
?????????? }
???????? // 任務(wù)2?? ?
?????????? ?
??????? }
?????? ?
??????? function checkone(){
??????????? var j=document.getElementById("wb").value; ? //得到你輸入的號
??????????? if(parseInt(j)>6||parseInt(j)<1){ ?//判斷是不是1到6號
??????????????? alert("請重新輸入") ?//不是彈出重新輸入
??????????? }
??????? document.getElementById("hobby"+j).checked = true; ?//各個選擇的ID不就是“hobby1”,“hobby2”等等嘛，其實就是假設(shè)j==2，"hobby"+j = "hobbyj" = “hobby2” 就得到對應(yīng)的選擇項2登山，然后打鉤
???????? // 任務(wù)3
?????? ?
??????? }