How do you JSON.stringify an ES6 Map?
I'd like to start using ES6 Map instead of JS objects but I'm being held back because I can't figure out how to JSON.stringify() a Map. My keys are guaranteed to be strings and my values will always be lists. Do I really have to write a wrapper method to serialize?
javascript ecmascript-6 io.js
asked Mar 16 '15 at 19:19
rynoprynop
23k196768
|
show 3 more comments
I'd like to start using ES6 Map instead of JS objects but I'm being held back because I can't figure out how to JSON.stringify() a Map. My keys are guaranteed to be strings and my values will always be lists. Do I really have to write a wrapper method to serialize?
javascript ecmascript-6 io.js
asked Mar 16 '15 at 19:19
rynoprynop
23k196768
interesting article on the topic 2ality.com/2015/08/es6-map-json.html
– David Chase
Apr 4 '18 at 15:58
I was able to get this to work. The results are on Plunkr at embed.plnkr.co/oNlQQBDyJUiIQlgWUPVP. The solution uses a JSON.stringify(obj, replacerFunction) which checks to see if a Map object is being passed and converts the Map object to a Javascript object (that JSON.stringify) will then convert to a string.
– PatS
Apr 10 '18 at 22:05
1
If your keys are guaranteed to be strings (or numbers) and your values arrays, you can do something like[...someMap.entries()].join(';'); for something more complex you could try something similar using something like[...someMap.entries()].reduce((acc, cur) => acc + `${cur[0]}:${/* do something to stringify cur[1] */ }`, '')
– user568458
May 10 '18 at 8:42
@Oriol What if it is possible for key name to be same as default properties?obj[key]may get you something unexpected. Consider the caseif (!obj[key]) obj[key] = newList; else obj[key].mergeWith(newList);.
– Franklin Yu
Nov 20 '18 at 15:20
@Brad Why did you reopen this?
– Bergi
Nov 24 '18 at 18:46
|
show 3 more comments
I'd like to start using ES6 Map instead of JS objects but I'm being held back because I can't figure out how to JSON.stringify() a Map. My keys are guaranteed to be strings and my values will always be lists. Do I really have to write a wrapper method to serialize?
javascript ecmascript-6 io.js
asked Mar 16 '15 at 19:19
rynoprynop
23k196768
I'd like to start using ES6 Map instead of JS objects but I'm being held back because I can't figure out how to JSON.stringify() a Map. My keys are guaranteed to be strings and my values will always be lists. Do I really have to write a wrapper method to serialize?
javascript ecmascript-6 io.js
javascript ecmascript-6 io.js
asked Mar 16 '15 at 19:19
rynoprynop
23k196768
asked Mar 16 '15 at 19:19
rynoprynop
23k196768
asked Mar 16 '15 at 19:19
rynoprynop
23k196768
asked Mar 16 '15 at 19:19
rynoprynop
23k196768
asked Mar 16 '15 at 19:19
rynoprynop
23k196768
23k196768
interesting article on the topic 2ality.com/2015/08/es6-map-json.html
– David Chase
Apr 4 '18 at 15:58
I was able to get this to work. The results are on Plunkr at embed.plnkr.co/oNlQQBDyJUiIQlgWUPVP. The solution uses a JSON.stringify(obj, replacerFunction) which checks to see if a Map object is being passed and converts the Map object to a Javascript object (that JSON.stringify) will then convert to a string.
– PatS
Apr 10 '18 at 22:05
1
If your keys are guaranteed to be strings (or numbers) and your values arrays, you can do something like[...someMap.entries()].join(';'); for something more complex you could try something similar using something like[...someMap.entries()].reduce((acc, cur) => acc + `${cur[0]}:${/* do something to stringify cur[1] */ }`, '')
– user568458
May 10 '18 at 8:42
@Oriol What if it is possible for key name to be same as default properties?obj[key]may get you something unexpected. Consider the caseif (!obj[key]) obj[key] = newList; else obj[key].mergeWith(newList);.
– Franklin Yu
Nov 20 '18 at 15:20
@Brad Why did you reopen this?
– Bergi
Nov 24 '18 at 18:46
|
show 3 more comments
interesting article on the topic 2ality.com/2015/08/es6-map-json.html
– David Chase
Apr 4 '18 at 15:58
I was able to get this to work. The results are on Plunkr at embed.plnkr.co/oNlQQBDyJUiIQlgWUPVP. The solution uses a JSON.stringify(obj, replacerFunction) which checks to see if a Map object is being passed and converts the Map object to a Javascript object (that JSON.stringify) will then convert to a string.
– PatS
Apr 10 '18 at 22:05
1
If your keys are guaranteed to be strings (or numbers) and your values arrays, you can do something like[...someMap.entries()].join(';'); for something more complex you could try something similar using something like[...someMap.entries()].reduce((acc, cur) => acc + `${cur[0]}:${/* do something to stringify cur[1] */ }`, '')
– user568458
May 10 '18 at 8:42
@Oriol What if it is possible for key name to be same as default properties?obj[key]may get you something unexpected. Consider the caseif (!obj[key]) obj[key] = newList; else obj[key].mergeWith(newList);.
– Franklin Yu
Nov 20 '18 at 15:20
@Brad Why did you reopen this?
– Bergi
Nov 24 '18 at 18:46
interesting article on the topic 2ality.com/2015/08/es6-map-json.html
– David Chase
Apr 4 '18 at 15:58
interesting article on the topic 2ality.com/2015/08/es6-map-json.html
– David Chase
Apr 4 '18 at 15:58
I was able to get this to work. The results are on Plunkr at embed.plnkr.co/oNlQQBDyJUiIQlgWUPVP. The solution uses a JSON.stringify(obj, replacerFunction) which checks to see if a Map object is being passed and converts the Map object to a Javascript object (that JSON.stringify) will then convert to a string.
– PatS
Apr 10 '18 at 22:05
I was able to get this to work. The results are on Plunkr at embed.plnkr.co/oNlQQBDyJUiIQlgWUPVP. The solution uses a JSON.stringify(obj, replacerFunction) which checks to see if a Map object is being passed and converts the Map object to a Javascript object (that JSON.stringify) will then convert to a string.
– PatS
Apr 10 '18 at 22:05
1
1
If your keys are guaranteed to be strings (or numbers) and your values arrays, you can do something like
[...someMap.entries()].join(';'); for something more complex you could try something similar using something like [...someMap.entries()].reduce((acc, cur) => acc + `${cur[0]}:${/* do something to stringify cur[1] */ }`, '')– user568458
May 10 '18 at 8:42
If your keys are guaranteed to be strings (or numbers) and your values arrays, you can do something like
[...someMap.entries()].join(';'); for something more complex you could try something similar using something like [...someMap.entries()].reduce((acc, cur) => acc + `${cur[0]}:${/* do something to stringify cur[1] */ }`, '')– user568458
May 10 '18 at 8:42
@Oriol What if it is possible for key name to be same as default properties?
obj[key] may get you something unexpected. Consider the case if (!obj[key]) obj[key] = newList; else obj[key].mergeWith(newList);.– Franklin Yu
Nov 20 '18 at 15:20
@Oriol What if it is possible for key name to be same as default properties?
obj[key] may get you something unexpected. Consider the case if (!obj[key]) obj[key] = newList; else obj[key].mergeWith(newList);.– Franklin Yu
Nov 20 '18 at 15:20
@Brad Why did you reopen this?
– Bergi
Nov 24 '18 at 18:46
@Brad Why did you reopen this?
– Bergi
Nov 24 '18 at 18:46
|
show 3 more comments
3 Answers
3
active
oldest
votes
You can't.
The keys of a map can be anything, including objects. But JSON syntax only allows strings as keys. So it's impossible in a general case.
My keys are guaranteed to be strings and my values will always be lists
In this case, you can use a plain object. It will have these advantages:
- It will be able to be stringified to JSON.
- It will work on older browsers.
- It might be faster.
edited Mar 16 '15 at 19:42
rynop
23k196768
answered Mar 16 '15 at 19:34
OriolOriol
160k38266372
6
for the curious-in the latest chrome, any map serializes into '{}'
– Capaj
Jan 6 '16 at 16:20
I have explained here what exactly I meant when I said "you can't".
– Oriol
Jan 29 '16 at 6:20
5
"It might be faster" - Do you have any source on that? I'm imagining a simple hash-map must be faster than a full blown object, but I have no proof. :)
– Lilleman
Feb 11 '16 at 18:01
1
@Xplouder That test uses expensivehasOwnProperty. Without that, Firefox iterates objects much faster than maps. Maps are still faster on Chrome, though. jsperf.com/es6-map-vs-object-properties/95
– Oriol
Mar 18 '16 at 13:49
1
True, seems that Firefox 45v iterates objects away faster than Chrome +49v. However Maps still wins vs objects in Chrome.
– Xplouder
Mar 18 '16 at 19:52
|
show 4 more comments
You can't directly stringify the Map instance as it doesn't have any properties, but you can convert it to an array of tuples:
jsonText = JSON.stringify(Array.from(map.entries()));
For the reverse, use
map = new Map(JSON.parse(jsonText));
answered Nov 24 '18 at 19:10
BergiBergi
375k60565897
add a comment |
While there is no method provided by ecmascript yet, this can still be done using JSON.stingify if you map the Map to a JavaScript primitive. Here is the sample Map we'll use.
const map = new Map();
map.set('foo', 'bar');
map.set('baz', 'quz');
Going to an JavaScript Object
You can convert to JavaScript Object literal with the following helper function.
const mapToObj = m => {
return Array.from(m).reduce((obj, [key, value]) => {
obj[key] = value;
return obj;
}, {});
};
JSON.stringify(mapToObj(map)); // '{"foo":"bar","baz":"quz"}'
Going to a JavaScript Array of Objects
The helper function for this one would be even more compact
const mapToAoO = m => {
return Array.from(m).map( ([k,v]) => {return {[k]:v}} );
};
JSON.stringify(mapToAoO(map)); // '[{"foo":"bar"},{"baz":"quz"}]'
Going to Array of Arrays
This is even easier, you can just use
JSON.stringify( Array.from(map) ); // '[["foo","bar"],["baz","quz"]]'
answered Jan 11 at 5:27
Evan CarrollEvan Carroll
36.1k24146247
add a comment |
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3 Answers
3
active
oldest
votes
3 Answers
3
active
oldest
votes
active
oldest
votes
active
oldest
votes
You can't.
The keys of a map can be anything, including objects. But JSON syntax only allows strings as keys. So it's impossible in a general case.
My keys are guaranteed to be strings and my values will always be lists
In this case, you can use a plain object. It will have these advantages:
- It will be able to be stringified to JSON.
- It will work on older browsers.
- It might be faster.
edited Mar 16 '15 at 19:42
rynop
23k196768
answered Mar 16 '15 at 19:34
OriolOriol
160k38266372
6
for the curious-in the latest chrome, any map serializes into '{}'
– Capaj
Jan 6 '16 at 16:20
I have explained here what exactly I meant when I said "you can't".
– Oriol
Jan 29 '16 at 6:20
5
"It might be faster" - Do you have any source on that? I'm imagining a simple hash-map must be faster than a full blown object, but I have no proof. :)
– Lilleman
Feb 11 '16 at 18:01
1
@Xplouder That test uses expensivehasOwnProperty. Without that, Firefox iterates objects much faster than maps. Maps are still faster on Chrome, though. jsperf.com/es6-map-vs-object-properties/95
– Oriol
Mar 18 '16 at 13:49
1
True, seems that Firefox 45v iterates objects away faster than Chrome +49v. However Maps still wins vs objects in Chrome.
– Xplouder
Mar 18 '16 at 19:52
|
show 4 more comments
You can't.
The keys of a map can be anything, including objects. But JSON syntax only allows strings as keys. So it's impossible in a general case.
My keys are guaranteed to be strings and my values will always be lists
In this case, you can use a plain object. It will have these advantages:
- It will be able to be stringified to JSON.
- It will work on older browsers.
- It might be faster.
edited Mar 16 '15 at 19:42
rynop
23k196768
answered Mar 16 '15 at 19:34
OriolOriol
160k38266372
6
for the curious-in the latest chrome, any map serializes into '{}'
– Capaj
Jan 6 '16 at 16:20
I have explained here what exactly I meant when I said "you can't".
– Oriol
Jan 29 '16 at 6:20
5
"It might be faster" - Do you have any source on that? I'm imagining a simple hash-map must be faster than a full blown object, but I have no proof. :)
– Lilleman
Feb 11 '16 at 18:01
1
@Xplouder That test uses expensivehasOwnProperty. Without that, Firefox iterates objects much faster than maps. Maps are still faster on Chrome, though. jsperf.com/es6-map-vs-object-properties/95
– Oriol
Mar 18 '16 at 13:49
1
True, seems that Firefox 45v iterates objects away faster than Chrome +49v. However Maps still wins vs objects in Chrome.
– Xplouder
Mar 18 '16 at 19:52
|
show 4 more comments
You can't.
The keys of a map can be anything, including objects. But JSON syntax only allows strings as keys. So it's impossible in a general case.
My keys are guaranteed to be strings and my values will always be lists
In this case, you can use a plain object. It will have these advantages:
- It will be able to be stringified to JSON.
- It will work on older browsers.
- It might be faster.
edited Mar 16 '15 at 19:42
rynop
23k196768
answered Mar 16 '15 at 19:34
OriolOriol
160k38266372
You can't.
The keys of a map can be anything, including objects. But JSON syntax only allows strings as keys. So it's impossible in a general case.
My keys are guaranteed to be strings and my values will always be lists
In this case, you can use a plain object. It will have these advantages:
- It will be able to be stringified to JSON.
- It will work on older browsers.
- It might be faster.
edited Mar 16 '15 at 19:42
rynop
23k196768
answered Mar 16 '15 at 19:34
OriolOriol
160k38266372
edited Mar 16 '15 at 19:42
rynop
23k196768
edited Mar 16 '15 at 19:42
rynop
23k196768
edited Mar 16 '15 at 19:42
rynop
23k196768
23k196768
answered Mar 16 '15 at 19:34
OriolOriol
160k38266372
answered Mar 16 '15 at 19:34
OriolOriol
160k38266372
answered Mar 16 '15 at 19:34
OriolOriol
160k38266372
160k38266372
6
for the curious-in the latest chrome, any map serializes into '{}'
– Capaj
Jan 6 '16 at 16:20
I have explained here what exactly I meant when I said "you can't".
– Oriol
Jan 29 '16 at 6:20
5
"It might be faster" - Do you have any source on that? I'm imagining a simple hash-map must be faster than a full blown object, but I have no proof. :)
– Lilleman
Feb 11 '16 at 18:01
1
@Xplouder That test uses expensivehasOwnProperty. Without that, Firefox iterates objects much faster than maps. Maps are still faster on Chrome, though. jsperf.com/es6-map-vs-object-properties/95
– Oriol
Mar 18 '16 at 13:49
1
True, seems that Firefox 45v iterates objects away faster than Chrome +49v. However Maps still wins vs objects in Chrome.
– Xplouder
Mar 18 '16 at 19:52
|
show 4 more comments
6
for the curious-in the latest chrome, any map serializes into '{}'
– Capaj
Jan 6 '16 at 16:20
I have explained here what exactly I meant when I said "you can't".
– Oriol
Jan 29 '16 at 6:20
5
"It might be faster" - Do you have any source on that? I'm imagining a simple hash-map must be faster than a full blown object, but I have no proof. :)
– Lilleman
Feb 11 '16 at 18:01
1
@Xplouder That test uses expensivehasOwnProperty. Without that, Firefox iterates objects much faster than maps. Maps are still faster on Chrome, though. jsperf.com/es6-map-vs-object-properties/95
– Oriol
Mar 18 '16 at 13:49
1
True, seems that Firefox 45v iterates objects away faster than Chrome +49v. However Maps still wins vs objects in Chrome.
– Xplouder
Mar 18 '16 at 19:52
6
6
for the curious-in the latest chrome, any map serializes into '{}'
– Capaj
Jan 6 '16 at 16:20
for the curious-in the latest chrome, any map serializes into '{}'
– Capaj
Jan 6 '16 at 16:20
I have explained here what exactly I meant when I said "you can't".
– Oriol
Jan 29 '16 at 6:20
I have explained here what exactly I meant when I said "you can't".
– Oriol
Jan 29 '16 at 6:20
5
5
"It might be faster" - Do you have any source on that? I'm imagining a simple hash-map must be faster than a full blown object, but I have no proof. :)
– Lilleman
Feb 11 '16 at 18:01
"It might be faster" - Do you have any source on that? I'm imagining a simple hash-map must be faster than a full blown object, but I have no proof. :)
– Lilleman
Feb 11 '16 at 18:01
1
1
@Xplouder That test uses expensive
hasOwnProperty. Without that, Firefox iterates objects much faster than maps. Maps are still faster on Chrome, though. jsperf.com/es6-map-vs-object-properties/95– Oriol
Mar 18 '16 at 13:49
@Xplouder That test uses expensive
hasOwnProperty. Without that, Firefox iterates objects much faster than maps. Maps are still faster on Chrome, though. jsperf.com/es6-map-vs-object-properties/95– Oriol
Mar 18 '16 at 13:49
1
1
True, seems that Firefox 45v iterates objects away faster than Chrome +49v. However Maps still wins vs objects in Chrome.
– Xplouder
Mar 18 '16 at 19:52
True, seems that Firefox 45v iterates objects away faster than Chrome +49v. However Maps still wins vs objects in Chrome.
– Xplouder
Mar 18 '16 at 19:52
|
show 4 more comments
You can't directly stringify the Map instance as it doesn't have any properties, but you can convert it to an array of tuples:
jsonText = JSON.stringify(Array.from(map.entries()));
For the reverse, use
map = new Map(JSON.parse(jsonText));
answered Nov 24 '18 at 19:10
BergiBergi
375k60565897
add a comment |
You can't directly stringify the Map instance as it doesn't have any properties, but you can convert it to an array of tuples:
jsonText = JSON.stringify(Array.from(map.entries()));
For the reverse, use
map = new Map(JSON.parse(jsonText));
answered Nov 24 '18 at 19:10
BergiBergi
375k60565897
add a comment |
You can't directly stringify the Map instance as it doesn't have any properties, but you can convert it to an array of tuples:
jsonText = JSON.stringify(Array.from(map.entries()));
For the reverse, use
map = new Map(JSON.parse(jsonText));
answered Nov 24 '18 at 19:10
BergiBergi
375k60565897
You can't directly stringify the Map instance as it doesn't have any properties, but you can convert it to an array of tuples:
jsonText = JSON.stringify(Array.from(map.entries()));
For the reverse, use
map = new Map(JSON.parse(jsonText));
answered Nov 24 '18 at 19:10
BergiBergi
375k60565897
answered Nov 24 '18 at 19:10
BergiBergi
375k60565897
answered Nov 24 '18 at 19:10
BergiBergi
375k60565897
answered Nov 24 '18 at 19:10
BergiBergi
375k60565897
375k60565897
add a comment |
add a comment |
While there is no method provided by ecmascript yet, this can still be done using JSON.stingify if you map the Map to a JavaScript primitive. Here is the sample Map we'll use.
const map = new Map();
map.set('foo', 'bar');
map.set('baz', 'quz');
Going to an JavaScript Object
You can convert to JavaScript Object literal with the following helper function.
const mapToObj = m => {
return Array.from(m).reduce((obj, [key, value]) => {
obj[key] = value;
return obj;
}, {});
};
JSON.stringify(mapToObj(map)); // '{"foo":"bar","baz":"quz"}'
Going to a JavaScript Array of Objects
The helper function for this one would be even more compact
const mapToAoO = m => {
return Array.from(m).map( ([k,v]) => {return {[k]:v}} );
};
JSON.stringify(mapToAoO(map)); // '[{"foo":"bar"},{"baz":"quz"}]'
Going to Array of Arrays
This is even easier, you can just use
JSON.stringify( Array.from(map) ); // '[["foo","bar"],["baz","quz"]]'
answered Jan 11 at 5:27
Evan CarrollEvan Carroll
36.1k24146247
add a comment |
While there is no method provided by ecmascript yet, this can still be done using JSON.stingify if you map the Map to a JavaScript primitive. Here is the sample Map we'll use.
const map = new Map();
map.set('foo', 'bar');
map.set('baz', 'quz');
Going to an JavaScript Object
You can convert to JavaScript Object literal with the following helper function.
const mapToObj = m => {
return Array.from(m).reduce((obj, [key, value]) => {
obj[key] = value;
return obj;
}, {});
};
JSON.stringify(mapToObj(map)); // '{"foo":"bar","baz":"quz"}'
Going to a JavaScript Array of Objects
The helper function for this one would be even more compact
const mapToAoO = m => {
return Array.from(m).map( ([k,v]) => {return {[k]:v}} );
};
JSON.stringify(mapToAoO(map)); // '[{"foo":"bar"},{"baz":"quz"}]'
Going to Array of Arrays
This is even easier, you can just use
JSON.stringify( Array.from(map) ); // '[["foo","bar"],["baz","quz"]]'
answered Jan 11 at 5:27
Evan CarrollEvan Carroll
36.1k24146247
add a comment |
While there is no method provided by ecmascript yet, this can still be done using JSON.stingify if you map the Map to a JavaScript primitive. Here is the sample Map we'll use.
const map = new Map();
map.set('foo', 'bar');
map.set('baz', 'quz');
Going to an JavaScript Object
You can convert to JavaScript Object literal with the following helper function.
const mapToObj = m => {
return Array.from(m).reduce((obj, [key, value]) => {
obj[key] = value;
return obj;
}, {});
};
JSON.stringify(mapToObj(map)); // '{"foo":"bar","baz":"quz"}'
Going to a JavaScript Array of Objects
The helper function for this one would be even more compact
const mapToAoO = m => {
return Array.from(m).map( ([k,v]) => {return {[k]:v}} );
};
JSON.stringify(mapToAoO(map)); // '[{"foo":"bar"},{"baz":"quz"}]'
Going to Array of Arrays
This is even easier, you can just use
JSON.stringify( Array.from(map) ); // '[["foo","bar"],["baz","quz"]]'
answered Jan 11 at 5:27
Evan CarrollEvan Carroll
36.1k24146247
While there is no method provided by ecmascript yet, this can still be done using JSON.stingify if you map the Map to a JavaScript primitive. Here is the sample Map we'll use.
const map = new Map();
map.set('foo', 'bar');
map.set('baz', 'quz');
Going to an JavaScript Object
You can convert to JavaScript Object literal with the following helper function.
const mapToObj = m => {
return Array.from(m).reduce((obj, [key, value]) => {
obj[key] = value;
return obj;
}, {});
};
JSON.stringify(mapToObj(map)); // '{"foo":"bar","baz":"quz"}'
Going to a JavaScript Array of Objects
The helper function for this one would be even more compact
const mapToAoO = m => {
return Array.from(m).map( ([k,v]) => {return {[k]:v}} );
};
JSON.stringify(mapToAoO(map)); // '[{"foo":"bar"},{"baz":"quz"}]'
Going to Array of Arrays
This is even easier, you can just use
JSON.stringify( Array.from(map) ); // '[["foo","bar"],["baz","quz"]]'
answered Jan 11 at 5:27
Evan CarrollEvan Carroll
36.1k24146247
edited Jan 11 at 5:42
answered Jan 11 at 5:27
Evan CarrollEvan Carroll
36.1k24146247
answered Jan 11 at 5:27
Evan CarrollEvan Carroll
36.1k24146247
answered Jan 11 at 5:27
Evan CarrollEvan Carroll
36.1k24146247
36.1k24146247
add a comment |
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interesting article on the topic 2ality.com/2015/08/es6-map-json.html
– David Chase
Apr 4 '18 at 15:58
I was able to get this to work. The results are on Plunkr at embed.plnkr.co/oNlQQBDyJUiIQlgWUPVP. The solution uses a JSON.stringify(obj, replacerFunction) which checks to see if a Map object is being passed and converts the Map object to a Javascript object (that JSON.stringify) will then convert to a string.
– PatS
Apr 10 '18 at 22:05
1
If your keys are guaranteed to be strings (or numbers) and your values arrays, you can do something like
[...someMap.entries()].join(';'); for something more complex you could try something similar using something like[...someMap.entries()].reduce((acc, cur) => acc + `${cur[0]}:${/* do something to stringify cur[1] */ }`, '')– user568458
May 10 '18 at 8:42
@Oriol What if it is possible for key name to be same as default properties?
obj[key]may get you something unexpected. Consider the caseif (!obj[key]) obj[key] = newList; else obj[key].mergeWith(newList);.– Franklin Yu
Nov 20 '18 at 15:20
@Brad Why did you reopen this?
– Bergi
Nov 24 '18 at 18:46