javascript语法基础,适用于初学者.ppt

 JavaScript 程序设计 第一章 JavaScript 语法基础 Lesson 5 主讲老师：王涛 QQ：164030235 Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. * 回顾 If条件句有哪几种格式，请描述下？ Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. * 本节目标 如果希望选择执行若干代码块中的一个，你可以使用 switch 语句： Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. * switch 语句 1 switch (表达式) { case 常量1 : JavaScript语句; break; case 常量2 : JavaScript语句; break; ... default : JavaScript语句; } 语法： Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. * switch语句 2 下拉列表框pay的选项和值 银行转帐－ 打6折 电话支付－ 打7折 邮政汇款－ 打8折 Q币支付－ 打9折 ..... var f=document.calc.pay.value; //支付方式代号 var grade; //折扣率 var total= parseFloat(numb1)*parseFloat(numb2); switch(parseInt(f)) { case 1: grade=0.6 ; //打6折优惠 break; case 2: …….同理其他方式打7折、八折 case 4: grade=0.9 ; //打9折优惠 break; default: alert(请重新选择支付方式！); return; } var money=total*grade; //根据折扣率，计算实际总价 document.calc.result.value=money; alert(您享受了+grade*10+折优惠！); ….. Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. * 常见错误1 SCRIPT language=javascript function compute() { x=5; var num1,num2; } /SCRIPT 变量可以不声明而直接赋值。如x=5; 不推荐使用，容易出错。 Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. * 常见错误2 SCRIPT language=javascript function compute(op) { var Num1,num2; num1=parseFloat(document.myform.txtNum1.value); num2=parseFloat(document.myform.txtNum2.value); if (op==+) document.myform.txtResult.value=num1+num2 ; if (op==-) document.myform.txtResult.value=num1-num2 ; } /SCRIPT JavaScript大小写非常