Question

48

How can I Display a JavaScript ES6 Map Object to Console?

rated 0 times [ 50] [ 2] / answers: 1 / hits: 62253 / 7 Years ago, tue, august 8, 2017, 12:00:00

Do I have to convert it to an object before I print it out?

I've tried

    const mapObject = new Map();

    

    mapObject.set(1, 'hello');

    

    console.log(JSON.stringify(mapObject));

    console.log(mapObject);

The results are always empty object.

When I use

console.log([...mapObject]);

It prints out an array format.

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dawnc

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3 Years ago

answered 7 Years ago jaquelineh · Accepted Answer

Note: This answer is only relevant to the repl.it sandbox environment OP is using

Since you said in the comments that you're using repl.it, there's a trick you can use to write your own logging strategy.

Note that you shouldn't use this trick in production, mainly because it edits a native prototype. In some Node environment, in your own code, it could be useful though.

The idea is to create an inspect method for Map that iterates over the entries:

Map.prototype.inspect = function() {

  return `Map(${mapEntriesToString(this.entries())})`

}



function mapEntriesToString(entries) {

  return Array

    .from(entries, ([k, v]) => `n  ${k}: ${v}`)

    .join() + n;

}

You can see that repl.it supports it here

console.log(new Map([[a, 1], [b, 2]]));

// Logs:

/*

Map(

  a: 1

  b: 2

)

*/