First item from a Map on JavaScript ES2015

Question

I have a Map like this:

const m = new Map();
m.set(\'key1\', {})
.
m.set(\'keyN\' {})

the Mapcan have 1 or many i

Answer 1

For the specific example you are wondering about, destructuring would be perfect.

let m = new Map();
m.set('key1', {});
m.set('key2', {});

let [[, obj]] = m;

e.g.

let [pair] = m;
let [key, obj] = pair;

is one option to destructure and then grab the value, but the easier option would be

let [obj] = m.values();

Answer 2

Use the Map.prototype.entries function, like this

const m = new Map();
m.set('key1', {})
m.set('keyN', {})

console.log(m.entries().next().value); // [ 'key1', {} ]

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If you want to get the first key, then use Map.prototype.keys, like this

console.log(m.keys().next().value); // key1

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Similarly if you want to get the first value, then you can use Map.prototype.values, like this

console.log(m.values().next().value); // {}

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The reason why we have to call next() on the returned values is that, all those functions return iterators. Read more about the iteration protocol here.

Answer 3

Also, that is correct for both Set and Map: you can convert anything to Array and then get any element by its index. Something like this:

const m = new Map();
m.set('key1', {});
m.set('key2', {});

console.log(Array.from(m)[0]); // ['key1', {}]

Answer 4

It could also done using spread feature at ES6 and next versions

const m = new Map();
m.set('key1', 1);
m.set('key2', 2);

console.log([...m][0]);    // ['key1', 1]                                                                     

                                                        
            

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