JSON.stringify deep objects
I need a function building a JSON valid string from any argument but :
- avoiding recursivity problem by not adding objects twice
- avoiding call stack size problem by truncating past a given depth
Generally it should be able to process big objects, at the cost of truncating them.
As reference, this code fails :
var json = JSON.stringify(window);
Avoiding recursivity problem is simple enough :
var seen = [];
return JSON.stringify(o, function(_, value) {
if (typeof value === 'object' && value !== null) {
if (seen.indexOf(value) !== -1) return;
else seen.push(value);
}
return value;
});
But for now, apart copying and changing Douglas Crockford's code to keep track of the depth, I didn't find any way to avoid stack overflow on very deep objects like window
or any event
. Is there a simple solution ?
Solution 1:
I did what I initially feared I'll have to do : I took Crockford's code and modified it for my needs. Now it builds JSON but handles
- cycles
- too deep objects
- too long arrays
- exceptions (accessors that can't legally be accessed)
In case anybody needs it, I made a GitHub repository : JSON.prune on GitHub
Here is the code :
// JSON.pruned : a function to stringify any object without overflow
// example : var json = JSON.pruned({a:'e', c:[1,2,{d:{e:42, f:'deep'}}]})
// two additional optional parameters :
// - the maximal depth (default : 6)
// - the maximal length of arrays (default : 50)
// GitHub : https://github.com/Canop/JSON.prune
// This is based on Douglas Crockford's code ( https://github.com/douglascrockford/JSON-js/blob/master/json2.js )
(function () {
'use strict';
var DEFAULT_MAX_DEPTH = 6;
var DEFAULT_ARRAY_MAX_LENGTH = 50;
var seen; // Same variable used for all stringifications
Date.prototype.toPrunedJSON = Date.prototype.toJSON;
String.prototype.toPrunedJSON = String.prototype.toJSON;
var cx = /[\u0000\u00ad\u0600-\u0604\u070f\u17b4\u17b5\u200c-\u200f\u2028-\u202f\u2060-\u206f\ufeff\ufff0-\uffff]/g,
escapable = /[\\\"\x00-\x1f\x7f-\x9f\u00ad\u0600-\u0604\u070f\u17b4\u17b5\u200c-\u200f\u2028-\u202f\u2060-\u206f\ufeff\ufff0-\uffff]/g,
meta = { // table of character substitutions
'\b': '\\b',
'\t': '\\t',
'\n': '\\n',
'\f': '\\f',
'\r': '\\r',
'"' : '\\"',
'\\': '\\\\'
};
function quote(string) {
escapable.lastIndex = 0;
return escapable.test(string) ? '"' + string.replace(escapable, function (a) {
var c = meta[a];
return typeof c === 'string'
? c
: '\\u' + ('0000' + a.charCodeAt(0).toString(16)).slice(-4);
}) + '"' : '"' + string + '"';
}
function str(key, holder, depthDecr, arrayMaxLength) {
var i, // The loop counter.
k, // The member key.
v, // The member value.
length,
partial,
value = holder[key];
if (value && typeof value === 'object' && typeof value.toPrunedJSON === 'function') {
value = value.toPrunedJSON(key);
}
switch (typeof value) {
case 'string':
return quote(value);
case 'number':
return isFinite(value) ? String(value) : 'null';
case 'boolean':
case 'null':
return String(value);
case 'object':
if (!value) {
return 'null';
}
if (depthDecr<=0 || seen.indexOf(value)!==-1) {
return '"-pruned-"';
}
seen.push(value);
partial = [];
if (Object.prototype.toString.apply(value) === '[object Array]') {
length = Math.min(value.length, arrayMaxLength);
for (i = 0; i < length; i += 1) {
partial[i] = str(i, value, depthDecr-1, arrayMaxLength) || 'null';
}
v = partial.length === 0
? '[]'
: '[' + partial.join(',') + ']';
return v;
}
for (k in value) {
if (Object.prototype.hasOwnProperty.call(value, k)) {
try {
v = str(k, value, depthDecr-1, arrayMaxLength);
if (v) partial.push(quote(k) + ':' + v);
} catch (e) {
// this try/catch due to some "Accessing selectionEnd on an input element that cannot have a selection." on Chrome
}
}
}
v = partial.length === 0
? '{}'
: '{' + partial.join(',') + '}';
return v;
}
}
JSON.pruned = function (value, depthDecr, arrayMaxLength) {
seen = [];
depthDecr = depthDecr || DEFAULT_MAX_DEPTH;
arrayMaxLength = arrayMaxLength || DEFAULT_ARRAY_MAX_LENGTH;
return str('', {'': value}, depthDecr, arrayMaxLength);
};
}());
An example of what can be done :
var json = JSON.pruned(window);
Note: Contrary to the code in this answer, the GitHub repository is updated when needed (documentation, compatibility, use as module in commonjs or node, specific serializations, etc.). It's a good idea to start from the repository if you need this pruning feature.
Solution 2:
If you're using Node.js you can use util.inspect
, which takes a depth argument.