How do I persist a ES6 Map in localstorage (or elsewhere)?

Question

var a = new Map([[ 'a', 1 ]]); a.get('a') // 1  var forStorageSomewhere = JSON.stringify(a); // Store, in my case, in localStorage.  // Later: var a = JSON.parse(forStorageSomewhere); a.get('a') // TypeError: undefined is not a function 

Unfortunatly JSON.stringify(a); simply returns '{}', which means a becomes an empty object when restored.

I found es6-mapify that allows up/down-casting between a Map and a plain object, so that might be one solution, but I was hoping I would need to resort to an external dependency simply to persist my map.

Answer 1

Assuming that both your keys and your values are serialisable,

localStorage.myMap = JSON.stringify(Array.from(map.entries())); 

should work. For the reverse, use

map = new Map(JSON.parse(localStorage.myMap));