The while loop is the simplest loop in JavaScript, its syntax is:
while (expr){
statement
}
This syntax indicates that as long as the expr expression is TRUE, the statement will be executed until expr is FALSE. The statement indicates the action or logic to be executed.
The following example uses a while loop to output 1 to 10:
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>php中文网(php.cn)</title>
<script type="text/javascript">
var i = 1;
while (i <= 10) {
document.write(i + "<br />");
i++;
}
</script>
</head>
<body>
</body>
</html>Running result:
1
2
3
4
5
6
7
8
9
10
##do while loop
The do while loop is very similar to the while loop. The only difference is that do while is guaranteed to be executed once, while while is If the expression does not hold, no operation may be performed.
do while loop syntax:
do { statement
}while (expr)
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>php中文网(php.cn)</title>
<script type="text/javascript">
var i = 1;
do {
document.write(i + "<br />");
i++;
} while (i <= 10);
</script>
</head>
<body>
</body>
</html>
Comparing for and while
If you have read the previous chapter about for loops, you will find that while loops are very similar to for loops.
Use for loop
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>php中文网(php.cn)</title>
</head>
<body>
<script>
cars=["BMW","Volvo","Saab","Ford"];
var i=0;
for (;cars[i];){
document.write(cars[i] + "<br>");
i++;
}
</script>
</body>
</html>Use while loop
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>php中文网(php.cn)</title>
</head>
<body>
<script>
cars=["BMW","Volvo","Saab","Ford"];
var i=0;
while (cars[i]){
document.write(cars[i] + "<br>");
i++;
}
</script>
</body>
</html>
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