Home > Developer > JavaScript
1. Ask for positive and
Requirements: Enter 10 numbers, find the positive number and positive numbers, and enter 999 to close the program:
<! DOCTYPE html>
<meta charset= "UTF-8" >
<title></title>
<script type= "Text/javascript" >
var sum=0
var p=0
for (Var i=1;i<=10;i++) {
var num=parseint (Prompt ("Please enter the" +i+ "number (enter 999 to end the program))
if (num==999) break;
else if (num<0) continue;
else sum=sum+num,p=p+1;
}
document.write ("The program terminates with a result of" +sum+ "number is" +p ")
</script>
<body>
</body>
2. Date of request
Requirement: Enter year, month, date to find out the day of the year
<! DOCTYPE html>
<meta charset= "UTF-8" >
<title></title>
<script type= "Text/javascript" >
var year=parseint (Prompt ("Please enter the Year")
var num1=year%4;
var num2=year%100;
var num3=year%400;
var s=28
num1==0&&num2!=0| | num3==0?s=29:s=28;
var sum=0
var month=parseint (Prompt ("Please enter month"))
if (month==1| | month==3| | month==5| | month==7| | month==8| |month==10| | MONTH==12)
{var day=parseint (prompt ("Please enter date (1-31)")
if (day>=1&&day<=31) day=day
else document.write ("date input error")
}
else if (month==4| | month==6| | month==9| | MONTH==11)
{var day=parseint (prompt ("Please enter date (1-30)")
if (day>=1&&day<=30) day=day
else document.write ("date input error")
}
else if (month==2)
{var day=parseint (prompt ("Please enter date (1-" +s+ "))
if (day>=1&&day<=s) day=day
else document.write ("date input error")
}
else document.write ("Month input error")
for (Var i=1;i<month;i++) {
if (i==1| | i==3| | i==5| | i==7| | i==8| |i==10| | I==12) {
sum+=31;
}else if (i==4| | i==6| | i==9| | i==11) {
sum+=30;
}else if (i==2) {
Sum+=s;
}
}
document.write (year+ "year" +month+ "month" +day+ "Day is the first" + (Sum+day) + "Day" of the year)
</script>
<body>
</body>
3. Common JavaScript logic statements
"If-else Structure"
1, the structure of the wording:
if (judging condition) {
Execute when condition is true
}else{
Execute if condition is false
}
2, if () the expression, the result of the operation should be:
①boolean:true true False False
②string: Non-empty string for vacuum string is False
③number:0 is false everything is not 0, are true
④null/nan/undefined: All is False
⑤object: All is True
3, else{} structure, can be omitted according to the specific circumstances;
var num = {};
if (num) {
Execute when condition is true
document.write (if condition is established);
}else{
Execute if condition is false
document.write ("If condition is not established");
}
Num<10?document.write ("If condition"):d ocument.write ("If condition is not established");
"Multiple If, ladder if"
1, the structure of the wording:
if (condition i) {
Condition One established
} else if (condition two) {
Condition one not established && condition II established
Else-if section, can have more than n
} else{
Condition one not established && condition two not established
}
2, multiple if structure, each judgment condition is mutually exclusive! Only one of the roads can be selected.
3, If/else {} can be omitted, but generally not advocated;
If you omit {}, the IF/ELSE structure contains code that is only the most recent line (the semicolon ends);
If you omit {}, the else structure always belongs to the nearest if structure in front of it.
var num2 = 5;
if (num2>5) {
document.write ("Input too large");
} else if (num2<5) {
document.write ("Input too small");
} else if (num2==5) {
document.write ("input correct");
}
if (num2==5) document.write ("Input too large");
if (num2==5) document.write ("Input too large");
else document.write ("11");
document.write ("22");
"Nested IF Structure"
1, the structure of the wording:
if (condition i) {
Condition One established
if (condition two) {
Condition I set up && Condition II also established
}else{
Condition One establishment && condition two not established
}
}else{
Condition one is not tenable
}
2, if structure can be multi-nesting, but in principle, not more than 3 layers
"Switch-case Structure"
1, the structure of the wording:
switch (expression) {
case constant Expression 1:
Statement 1;
Break
Case constant Expression 2:
Statement 2;
Break
......
Default
Statement n
Break
}
2. Precautions:
The expression in ①switch (), and the expression following each case, can be any of the data types supported by JS (objects and arrays do not work);
All constant expressions following the ②case must be different, otherwise only the first one will be executed;
The constants after ③case can be any data type; different case of the same switch structure can be many different data types;
④switch in the judgment of the time, the use of a congruent judgment = = =.
⑤break function: After executing the case code, jump out of the current switch structure;
The consequences of missing a break: Start with the correct case and execute all case and default in turn. Reason: ⑥↓
⑥switch structure When judging, will only judge the correct answer, when the correct case is encountered, will not judge the subsequent project. Execute in turn.
⑦switch structures are executed faster than multiple if structures. In a multi-channel branch, you can prioritize the use of the switch structure.
var num4 = 5;
Switch (NUM4) {
Case 4:
document.write ("This is a case block of 9!") ");
Break
Case 5:
document.write ("This is a case block of 10!") ");
Break
Case 6:
document.write ("This is a case block of 11!") ");
Break
Default
document.write ("This is the case block of default!") ");
Break
}
JavaScript program case
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