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D3.js | d3.map.keys() Function
  • Last Updated : 28 Jun, 2019

The map.keys() function in D3.js is used to return an array of string keys for every entry in the created map. The order of the returned keys is arbitrary.

Syntax:

map.keys()

Parameters: This function does not accept any parameters.

Return Value: This function returns an array of string keys for every entry in the created map.

Below programs illustrate the d3.map.keys() function in D3.js:



Example 1:

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<!DOCTYPE html>
<html>
  
<head>
    <title>d3.map.keys() function</title>
  
    <script src='https://d3js.org/d3.v4.min.js'></script>
</head>
  
<body>
    <script>
          
        // Creating a map
        var map = d3.map({"Ram": 5, "Geeks": 10, "gfg": 15});
        
        // Calling the map.keys() function
        A = map.keys();
        
        // Getting an array of string keys for
        // every entry in the map.
        console.log(A);
    </script>
</body>
  
</html>

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Output:

["Ram", "Geeks", "gfg"]

Example 2:

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<!DOCTYPE html>
<html>
  
<head>
    <title>d3.map.keys() function</title>
  
    <script src='https://d3js.org/d3.v4.min.js'></script>
</head>
  
<body>
    <script>
          
        // Creating some maps
        var map1 = d3.map({"Ram": 5});
        var map2 = d3.map({"Geeks": 10});
        var map3 = d3.map({"Ram": 5, "Geeks": 10});
        var map4 = d3.map();
        
        // Calling the map.keys() function
        A = map1.keys();
        B = map2.keys();
        C = map3.keys();
        D = map4.keys();
        
        // Getting an array of string keys for
        // every entry in the map.
        console.log(A);
        console.log(B);
        console.log(C);
        console.log(D);
    </script>
</body>
  
</html>

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Output:

["Ram"]
["Geeks"]
["Ram", "Geeks"]
[]

Ref: https://devdocs.io/d3~5/d3-collection#map_keys

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