Serialization
In this chapter you will learn:
- How to use JSON.stringify() to convert object to JSON string
- How to control the string indention in JSON
- How to indent JSON string value during serialization
- How to use toJSON() Method
JSON.stringify()
The JSON.stringify() method accepts two
arguments in addition to the object to serialize.
The first argument is a filter, which can be either an array or a function. The second argument is an option for indenting the resulting JSON string.
If the argument is an array, JSON.stringify() includes
only object properties that are listed in the array.
<!DOCTYPE html><!--from ja v a2s. co m-->
<html>
<head>
<script type="text/javascript">
var book = {
"title": "JavaScript",
"authors": ["J" ],
edition: 3,
year: 2011
};
var jsonText = JSON.stringify(book, ["title", "edition"]);
document.writeln(jsonText);
</script>
</head>
<body>
</body>
</html>
When the second argument is a function. The provided function receives two arguments: the property key name and the property value.
You can look at the key to determine what to do with the property. The key may be an empty string if a value isn't part of a key-value pair.
The undefined property is omitted from the result in the JSON.stringify method.
<!DOCTYPE html><!--from j a v a 2 s . c o m-->
<html>
<head>
<script type="text/javascript">
var book = {
"title": "JavaScript",
"authors": ["J"],
edition: 3,
year: 2011
};
var jsonText = JSON.stringify(book, function(key, value){
switch(key){
case "authors":
return value.join(",")
case "year":
return 2012;
case "edition":
return undefined;
default:
return value;
}
});
document.writeln(jsonText);
</script>
</head>
<body>
</body>
</html>
String Indentation
The third argument of JSON.stringify()
controls indentation and white space.
When this argument is a number, it represents
the number of spaces to indent each level.
The following code indents each level by four spaces:
<!DOCTYPE html><!--from java2s. c om-->
<html>
<head>
<script type="text/javascript">
var book = {
"title": "JavaScript",
"authors": [ "J" ],
edition: 3,
year: 2011
};
var jsonText = JSON.stringify(book, null, 4);
document.writeln("<pre>"+jsonText+"</pre>");
</script>
</head>
<body>
</body>
</html>
Indent with string value
If the indentation argument is a string, the string is used as the indentation character for the JSON string instead of a space.
<!DOCTYPE html><!--from j a v a 2 s.com-->
<html>
<head>
<script type="text/javascript">
var book = {
"title": "JavaScript",
"authors": [ "J" ],
edition: 3,
year: 2011
};
var jsonText = JSON.stringify(book, null, " - -");
document.writeln("<pre>"+jsonText+"</pre>");
</script>
</head>
<body>
</body>
</html>
toJSON() Method
You can add a toJSON() method to the object and have it return the proper JSON representation. The native Date object has a toJSON() method that converts JavaScript Date objects into an ISO 8601 date string.
A toJSON() method can be added to any object, for example:
<!DOCTYPE html><!--from j a va2 s . c o m-->
<html>
<head>
<script type="text/javascript">
var book = {
"title": "JavaScript",
"authors": ["J"],
edition: 3,
year: 2011,
toJSON: function(){
return this.title;
}
};
var jsonText = JSON.stringify(book);
document.writeln("<pre>"+jsonText+"</pre>");
</script>
</head>
<body>
</body>
</html>
Next chapter...
What you will learn in the next chapter: