D3.js node.count() Function

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The node.count() function of D3.js library is used to count the number of leaves under a particular node and append it as a value property to the object. If the node given is itself a leaf node then the count is one.

Syntax:

node.count();

Parameters: This function does not take any parameter.

Return Value: This function returns an object.

Below given are a few examples of the function given above.

Example 1: The following example demonstrates counting leaves for the root node.

HTML

<!DOCTYPE html> 
<html lang="en"> 
  
<head> 
    <meta charset="UTF-8" /> 
    <meta name="viewport" path1tent= 
    "width=device-width, initial-scale = 1.0" /> 
  
    <script src="https://d3js.org/d3.v4.min.js"> 
    </script> 
</head> 
  
<body> 
    <script> 
        // Constructing a tree 
        var tree = { 
            name: "rootNode", 
            children: [ 
                { 
                    name: "child1" 
                }, 
                { 
                    name: "child2", 
                    children: [ 
                        { 
                            name: "grandchild1", 
                            children: [ 
                                { name: "grand_granchild1_1" }, 
                                { name: "grand_granchild1_2" } 
                            ] 
                        }, 
                        { 
                            name: "grandchild2", 
                            children: [ 
                                { name: "grand_granchild2_1" }, 
                                { name: "grand_granchild2_2" } 
                            ] 
                        }, 
                    ] 
                } 
            ] 
        }; 
  
        var obj = d3.hierarchy(tree); 
  
        // Using node.count() Function 
        var count = obj.count(); 
        console.log("The number of leaves for root" 
                + " node are: ", count.value); 
    </script> 
</body> 
  
</html> 

Output:

Example 2: The following code demonstrates counting number of leaves for any node.

HTML

<!DOCTYPE html> 
<html lang="en"> 
  
<head> 
    <meta charset="UTF-8" /> 
    <meta name="viewport" path1tent= 
        "width=device-width, initial-scale = 1.0" /> 
    <script src="https://d3js.org/d3.v4.min.js"> 
    </script> 
</head> 
  
<body> 
    <script> 
        // Constructing a tree 
        var tree = { 
            name: "rootNode", // Root node 
            children: [ 
                { 
                    name: "child1" // Child of root node 
                }, 
                { 
                    name: "child2", // Child of root node 
                    children: [ 
                        { 
                            // Child of child2 
                            name: "grandchild1", 
                            children: [ 
                                // Child of grandchild1 
                                { name: "grand_granchild1_1" }, 
                                // Child of grandchild1  
                                { name: "grand_granchild1_2" } 
                            ] 
                        }, 
                        { 
                            name: "grandchild2", 
                            children: [ 
                                // Child of grandchild2 
                                { name: "grand_granchild2_1" }, 
                                // Child of grandchild2 
                                { name: "grand_granchild2_2" } 
                            ] 
                        }, 
                    ] 
                } 
            ] 
        }; 
  
        var obj = d3.hierarchy(tree); 
        var grandchild2 = obj.children[1].children[1]; 
  
        // Using node.count() function 
        var count = grandchild2.count(); 
        console.log("The number of leaves for " 
            + "grandchild2 are: ", count.value); 
    </script> 
</body> 
  
</html> 