JavaScript學習 - 基礎(四) - 控制語句/異常處理
阿新 • • 發佈：2018-10-31
控制語句
if-else 語句
<script>
//控制語句
//if-else格式:
var x = 1
if(x==1){
console.log("this is if")
}else if(x>1){
console.log("this is else if")
}else {
console.log("this else")
}
</script>
switch語句
<script>
//switch語句
var x = 8;
switch (x){
case 1:alert("this 1");break;
case 2:alert("this 2");break;
case 3:alert("this 3");break;
case 4:alert("this 4");break;
case 5:alert("this 5");break;
case 6:alert("this 6");break;
for迴圈語句
<script>
// for迴圈:for while
// 基本格式:
for(初始化;條件;增量){語句}
for(i=1;i<100;i++){
document.write(i)
document.write('<br>')
}
var x = [1,2,3,4,5,6]
<body>
<p>A</p>
<p>B</p>
<p>C</p>
<p>D</p>
<p>E</p>
<p>F</p>
<p>G</p>
</body>
//不建議使用的原因
var x2 = document.getElementsByTagName('p')
for(i in x2) {
document.write('this i,輸出:' + i);
document.write('<br>');
document.write('this x[i],輸出:' + x2[i]);
document.write('<br>');
document.write('----------------------');
document.write('<br>');
}
// this i,輸出:0
// this x[i],輸出:[object HTMLParagraphElement]
// ----------------------
// this i,輸出:1
// this x[i],輸出:[object HTMLParagraphElement]
// ----------------------
// this i,輸出:2
// this x[i],輸出:[object HTMLParagraphElement]
// ----------------------
// this i,輸出:3
// this x[i],輸出:[object HTMLParagraphElement]
// ----------------------
// this i,輸出:4
// this x[i],輸出:[object HTMLParagraphElement]
// ----------------------
// this i,輸出:5
// this x[i],輸出:[object HTMLParagraphElement]
// ----------------------
// this i,輸出:6
// this x[i],輸出:[object HTMLParagraphElement]
// ----------------------
// this i,輸出:length
// this x[i],輸出:7
// ----------------------
// this i,輸出:item
// this x[i],輸出:function item() { [native code] }
// ----------------------
// this i,輸出:namedItem
// this x[i],輸出:function namedItem() { [native code] }
</script>
while迴圈語句
<script>
//while 迴圈
var i=0;j=0;
while(i<201){
j +=i
i++;
}
document.write(j)
</script>
異常處理
<script>
//異常
//try{主程式}catch(異常){執行}finally{無論是否異常都執行}
//主動丟擲異常 throw Error("xxxx")
try{
throw Error("報錯了!!!")
document.write("OK")
}
catch (e) {
document.write("異常")
}
finally {
document.write("OK and OK")
}
</script>