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JavaScript Map keys() Method
  • Last Updated : 16 Jul, 2020

Below is the basic example of the Map.keys() method.

Javascript

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<script>
  let mp=new Map()
  mp.set("a",11);
  mp.set("b",2);
  mp.set("c",5);
  console.log(mp.keys());
</script>

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Output:

MapIterator {"a", "b", "c"}

The Map.keys() method is used to extract the keys from a given map object and return the iterator object of keys. The keys are returned in the order they were inserted.

Syntax: 

Map.keys()

Parameters: This method does not accept any parameters.



Returns: This returns the iterator object that contains keys in the map.

Code for the above method is provided below:
Program 1:

HTML

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<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" 
        content="width=device-width,
                 initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <ul class="list">
  </ul>
  <script>
    // Creating a map using Map object
    let mp=new Map()
    // Adding key value pairs to the map mp
    mp.set("a",1);
    mp.set("b",2);
    mp.set("c",22);
    mp.set("d",12);
    console.log("Type of mp.keys() is: ",typeof (mp.keys()));
    console.log("Keys in map mp are: ",mp.keys());
  </script>
</body>
</html>

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Output:

Program 2: Updating the value of the key in the map and printing values using the iterator object.

HTML

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<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" 
        content="width=device-width,
                 initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <ul class="list">
  </ul>
  <script>
    // Creating a map using Map object
    let mp=new Map()
    // Adding key value pairs to the map mp
    mp.set("q",1);
    mp.set("w",2);
    // Value of key "q" is updated to 22
    mp.set("q",22);
    mp.set("d",22);
    mp.set("c",12);
    let it=mp.keys();
    // Logginfg iterator object
    console.log(it);
    console.log(it.next().value)
    // Iterator pointing to next key and 
    // printing the value
    console.log(it.next().value)
  </script>
</body>
</html>

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Output: 

Supported Browsers: 

  • Chrome
  • Opera
  • Edge
  • Firefox
  • Safari

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