tryjson
v1.1.4
Published
Try to parse a string as JSON and return undefined on failure
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Readme
node tryjson
TL;DR
JSON.parse / JSON.stringify
// this can crash your program
// you need try/catch:
object = JSON.parse(string);
// this can crash your program
// you need try/catch:
string = JSON.stringify(object);
tryjson.parse / tryjson.stringify
// no need for try/catch:
string = tryjson.stringify(object);
// no need for try/catch:
object = tryjson.parse(string);
Why
Not everyone knows that you should always run JSON.parse
inside of a try/catch
block or otherwise you risk your application crashing on bad input. Most of the examples of using JSON.parse
posted online never does that. People usually assume that you will get undefined
on bad or empty input but you don't.
Remember: Always try { JSON.parse() }
or use tryjson.parse()
This module works like many people assume that the built-in JSON
works and can simplify some common code.
People usually write:
object = JSON.parse(string);
when they mean:
try {
object = JSON.parse(string);
} catch (e) {
object = undefined;
}
and now they can write it as:
object = tryjson.parse(string);
or even as:
object = JSON.parse(string);
if you want to locally override JSON
with:
var JSON = require('tryjson');
You can even get a different value than the default undefined
for invalid JSON:
object = JSON.parse(string, {error: 'Invalid JSON'});
How it works
This module works like JSON.parse
(and in fact it uses JSON.parse
) but instead of throwing exceptions it returns undefined
on failure (or some other fallback value if provided). This is not always a desired behaviour but sometimes it is.
There is also a stringify
method that works like JSON.stringify
but instead of throwing exceptions on circular structures it returns "null"
(or a JSON representation of some other fallback value if provided) - which, again, may not be what you always want but sometime it is and you can use this module to simplify your code in those cases.
Methods
parse(string)
Returns the result of parsing string
as JSON or undefined
if it cannot be parsed.
parse(string, fallback)
Returns the result of parsing string
as JSON or the value of fallback
if it cannot be parsed.
stringify(value)
Returns the JSON representation of value
or the JSON representation of null
if value
cannot be represented as JSON (e.g. contains circular references).
stringify(value, fallback)
Returns the JSON representation of value
or the JSON representation of fallback
if value
cannot be represented as JSON (or the JSON representation of null
if fallback
cannot be represented as JSON as well).
Rationale
Why tryjson.parse
returns undefined
for invalid JSON by default? Because a valid JSON can never be parsed to undefined
so you can test it reliably for that value with value === undefined
to know if it was invalid. You can specify a custom fallback value as a second argument.
Why tryjson.stringify
returns "null"
for objects that cannot be serialized by default? Because "null"
is a valid JSON string so it can always be parsed without errors and is still easy to test for null
value. Note that this time, getting "null" does not necessarily mean that the object couldn't be serialized because it might have been originally equal to null
as well. You can specify a custom fallback value as a second argument - it will be stringified to JSON if possible, or the string "null"
will be returned. It always returns a valid JSON string.
Installation
Install to use in your Node project, updating the dependencies in package.json:
npm install tryjson --save
Examples
Basic usage:
Parsing
var tryjson = require('tryjson');
tryjson.parse('{"a":1,"b":2}');
// returns object: { a: 1, b: 2 }
tryjson.parse('{"a":1,"b":2');
// returns value: undefined
Stringification
var tryjson = require('tryjson');
var x = {a: 1};
tryjson.stringify(x);
// returns string: '{"a":1}'
x.b = x;
tryjson.stringify(x);
// returns string: 'null'
Testing returned values
var object = tryjson.parse(string);
if (object === undefined) {
// the string was invalid JSON
}
if (object == null) {
// the string was either invalid JSON
// or "null"
}
if (!object) {
// the string was either invalid JSON,//
// "null", "false" or "0"
}
Custom fallback values:
tryjson.parse('{"a":1,"b":2}', {err: 'bad json'});
// returns object: { a: 1, b: 2 }
tryjson.parse('{"a":1,"b":2', {err: 'bad json'});
// returns object: { err: 'bad json' }
var x = {a: 1};
tryjson.stringify(x, {err: 'bad object'});
// returns string: '{"a":1}'
x.b = x;
tryjson.stringify(x, {err: 'bad object'});
// returns string: '{"err":"bad object"}'
// invalid object and invalid fallback:
tryjson.stringify(x, x);
// returns string: 'null'
Issues
For any bug reports or feature requests please post an issue on GitHub.
Author
Rafał Pocztarski - https://github.com/rsp
License
MIT License (Expat). See LICENSE.md for details.