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JS (Coursera): For Loops

2016-06-06 09:11 344 查看

For Loops

You’ll be able to create different kinds of for loop

for

clearly shows the start and end values

is especially good for handling a series of data

(data_structure.length tells you how many items data_structure contains)

<html><head>
<script>
var continents=["Australia", "Africa",
"Antarctica", "Eurasia", "America"];
var response, count=0;
for (var index=0; index < continents.length;
index++) {
response = confirm("Have you been to " +
continents[index] + "?");
if (response) count++;
}
alert("You have been to " + count +
" continents!");
</script>
</head></html>


for…in

gives you the index of each item

<!doctype html>
<html><head>
<script>
var continents=["Australia", "Africa",
"Antarctica", "Eurasia", "America"];
var response, count=0;
for (var index in continents) {
response=confirm("Have you been to "
+ continents[index] + "?");
if (response) count++;
}
alert("You have been to " + count +
" continents!");
</script>
</head></html>


this example shows how for…in can be used to access the content of a data structure(like json).

<!doctype html>
<html><head>
<title>Example of for in</title>
<script>
var response, count=0;
var onePerson = { initials:"DR", age:40,job:"Professor" };

for (var property in onePerson) {
alert(property + "=" + onePerson[property]);
}
</script>
</head></html>


for…of

gives you each item(not index)

<!doctype html>
<html><head>
<title>Example of for of</title>
<script>
var continents=["Australia", "Africa",
"Antarctica", "Eurasia", "America"];
var response, count=0;
for (var continent of continents) {
response = confirm("Have you been to " +
continent + "?");
if (response) count++;
}
alert("You have been to " + count + " continents!");
</script>
</head></html>


Loop Control

You’ll be able to control loops in two new ways

break
continue


break

break

totally stops the loop

continue

continue

stops the current iteration
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标签：  javascript loops
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