[javascript] How to convert a plain object into an ES6 Map?

For some reason I can't find this simple thing in the MDN docs (maybe I'm just missing it).

I expected this to work:

const map = new Map({foo: 'bar'});

map.get('foo'); // 'bar'

...but the first line throws TypeError: (var)[Symbol.iterator] is not a function

How do I make a Map from a plain object? Do I really have to first convert it into an array of arrays of key-value pairs?

The answer by Nils describes how to convert objects to maps, which I found very useful. However, the OP was also wondering where this information is in the MDN docs. While it may not have been there when the question was originally asked, it is now on the MDN page for Object.entries() under the heading Converting an Object to a Map which states:

Converting an Object to a Map

The new Map() constructor accepts an iterable of entries. With Object.entries, you can easily convert from Object to Map:

const obj = { foo: 'bar', baz: 42 }; 
const map = new Map(Object.entries(obj));
console.log(map); // Map { foo: "bar", baz: 42 }

Do I really have to first convert it into an array of arrays of key-value pairs?

No, an iterator of key-value pair arrays is enough. You can use the following to avoid creating the intermediate array:

function* entries(obj) {
    for (let key in obj)
        yield [key, obj[key]];
}

const map = new Map(entries({foo: 'bar'}));
map.get('foo'); // 'bar'

const myMap = new Map(
    Object
        .keys(myObj)
        .map(
            key => [key, myObj[key]]
        )
)

Alternatively you can use the lodash toPairs method:

const _ = require('lodash');
const map = new Map(_.toPairs({foo: 'bar'}));

ES6

convert object to map:

const objToMap = (o) => new Map(Object.entries(o));

convert map to object:

const mapToObj = (m) => [...m].reduce( (o,v)=>{ o[v[0]] = v[1]; return o; },{} )

Note: the mapToObj function assumes map keys are strings (will fail otherwise)