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

Question

I'm using repl.it/languages/javascript.

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.

Answer 1

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
)
*/