變量:(variable)
JavaScript可以直接對變量進行賦值而不要事先聲明
JavaScript語言裏,變量和其他元素的名字都是區分大小寫的
JavaScript變量允許包含字母、數字、美元符號和下劃線,但不允許數字開頭
爲什麼不能以數字開頭?
避免計算機運算的混亂,乘法省略乘號,因此強制不能使用數字
<!doctype html> <html> <head> <meta charset="utf-8"> <title> javascript頁面</title> <script type="text/javascript"> var hello = "你好"; var hello = "大家好"; document.write(hello); </script> </head> <body> </body> </html> |
數據類型:
JavaScript類型聲明和其他語言一樣,但是JavaScript是弱類型語言,不需要聲明類型
弱類型就是意味着,可以隨意改變某個變量的數據類型
<script type="text/javascript"> var num = 100; document.write(num); document.write("<br/>"); document.write(num+1); document.write("<br/>"); document.write(num+"1"); </script> |
數據類型:字符串、數值、布爾值、數組
轉義字符:字符串自動轉義 \
<script type="text/javascript"> var name = "小明"; document.write(name); document.write("<br/>"); var name = "小\''明"; document.write(name); document.write("<br/>"); var name = '"小明"'; document.write(name);//"小明" </script> |
數組聲明:
<!doctype html> <html> <head> <meta charset="utf-8"> <title>第一個javascript頁面</title> <script type="text/javascript"> var week = new Array("sunday","monday","tuesday","wednesday","thirsday","friday","staturday"); document.write(week[0]); document.write("<br/>"); document.write(week. length); </script> </head> <body> </body> </html> |
運算符:
算術運算符加減乘除取餘 ++ --
比較運算符> <>= <= == !=\
邏輯運算符&& || ! &
條件語句:
If語句 while() do… While () for () switch () case
函數:
需要多次使用同一組語句,可以打包成一個函數
<!doctype html> <html> <head> <meta charset="utf-8"> <title>第一個javascript頁面</title> <script type="text/javascript"> var n =Math. floor( Math. random()*10000); document.write(n); document.write("隨機數字爲<br/>"); while(n != 1){ if (n%2 == 1) { n = n * 3 + 1; }else{ n/=2; } document.write(n); document.write("<br/>"); } </script> </head> <body> </body> </html> |