The map.has() function in D3.js is used to return true if the created map has an entry for specified key string. The value of map.has() function may be null or undefined.
Syntax:
map.has(key)
Parameters: This function accepts single parameter key which is specified the key string.
Return Value: This function returns true if created map has an entry for the specified key string. The value may be null or undefined.
Below programs illustrate the d3.map.has() function in D3.js:
Example 1:
<!DOCTYPE html> <html>   <head>     <title>d3.map.has() function</title>   </head>   <body>     <script>                   // Creating a map         var map = d3.map({"Ram": 5});                 // Calling the map.has() function         A = map.has("Ram");         B = map.has("Geeks");                 // Getting the true if the map         // has an entry for the specified key string         // else false         console.log(A);         console.log(B);     </script> </body>   </html> |
Output:
true false
Example 2:
<!DOCTYPE html> <html>   <head>     <title>d3.map.has() function</title>   </head>   <body>     <script>                   // Creating a map         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.has() function         A = map1.has("Ram");         B = map2.has("Geeks");         C = map3.has("Geeks");         D = map3.has("Ram");         E = map4.has("Geeks");                 // Getting the true if the map         // has an entry for the specified key string         // else false         console.log(A);         console.log(B);         console.log(C);         console.log(D);         console.log(E);     </script> </body>   </html> |
Output:
true true false true false
Ref: https://devdocs.io/d3~5/d3-collection#map_has
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