Question

How to combine 2 maps into a third map in JavaScript

Answer 1

// Objects
const map1 = { a: "aaa", b: "bbb" };
const map2 = { c: "ccc", b: "XYZ", d: "ddd" }; // 'b' will be overwritten


const combined = { ...map1, ...map2 };

console.log(combined);



/*
run:

{ a: 'aaa', b: 'XYZ', c: 'ccc', d: 'ddd' }

*/

 

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Answer 2

const map1 = new Map([
  ["a", "aaa"],
  ["b", "bbb"]
]);

const map2 = new Map([
  ["c", "ccc"],
  ["b", "XYZ"], // Overwrites 'b'
  ["d", "ddd"]
]);

const combined = new Map([...map1, ...map2]);

console.log(combined);



/*
run:

Map(4) { 'a' => 'aaa', 'b' => 'XYZ', 'c' => 'ccc', 'd' => 'ddd' }

*/

 

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Answer 3

const map1 = new Map([
  ["a", "aaa"],
  ["b", "bbb"]
]);

const map2 = new Map([
  ["c", "ccc"],
  ["b", "XYZ"], // Overwrites 'b'
  ["d", "ddd"]
]);

const combined = new Map(map1);

for (const [key, value] of map2) {
  if (combined.has(key)) {
    combined.set(key, combined.get(key) + ", " + value); // Merge values
  } else {
    combined.set(key, value);
  }
}

console.log(combined);



/*
run:

Map(4) { 'a' => 'aaa', 'b' => 'bbb, XYZ', 'c' => 'ccc', 'd' => 'ddd' }

*/

 

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