D3.js node.eachBefore() Function

Last Updated : 31 Aug, 2020

The node.eachBefore() function is used to invoke a particular function for each node but in a pre-order-traversal order. It visits each node in pre-traversal order and performs an operation on that particular node and each of its descendants.

Syntax:

node.eachBefore(function);

Parameters: This function accepts a single parameter as mentioned above and described below:

function: This is the function that is to be invoked for each node.

Return Value: This function does not return anything.

Example 1:

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 = { 
            // Root node 
            name: "rootNode", 
            children: [ 
                { 
                    // Child of root node 
                    name: "child1", 
                    value: 2 
                }, 
                { 
                    // Child of root node 
                    name: "child2", 
                    value: 3, 
                    children: [ 
                        { 
                            // Child of child2 
                            name: "grandchild1", 
                            value: 1, 
                            children: [ 
                                { 
                                    // Child of grandchild1 
                                    name: "grand_granchild1_1", 
                                    value: 4 
                                }, 
                                { 
                                    // Child of grandchild1 
                                    name: "grand_granchild1_2", 
                                    value: 5 
                                } 
                            ] 
                        }, 
                        { 
                            name: "grandchild2", 
                            children: [ 
                                { 
                                    // Child of grandchild2 
                                    name: "grand_granchild2_1" 
                                }, 
                                { 
                                    // Child of grandchild2 
                                    name: "grand_granchild2_2" 
                                } 
                            ] 
                        } 
                    ] 
                } 
            ] 
        }; 
  
        var obj = d3.hierarchy(tree); 
  
        const BFS = []; 
  
        obj.eachBefore(d => BFS.push 
            ( 
                " ".repeat(d.depth)  
                    + `${d.depth}: ${d.data.name}` 
            )); 
  
        BFS.forEach((e) => { 
            console.log("level:", e); 
        }) 
    </script> 
</body> 
  
</html> 

Output:

Example 2:

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> 
        var obj = d3.hierarchy({ 
            // Root node 
            name: "rootNode", 
            children: [ 
                { 
                    // Child of root node 
                    name: "child1", 
                    value: 2 
                }, 
                { 
                    // Child of root node 
                    name: "child2", 
                    value: 3, 
                    children: [ 
                        { 
                            // Child of child2 
                            name: "grandchild1", 
                            value: 1, 
                            children: [{ 
                                // Child of grandchild1 
                                name: "grand_granchild1_1", 
                                value: 4 
                            }, 
  
                            { 
                                // Child of grandchild1 
                                name: "grand_granchild1_2", 
                                value: 5 
                            }] 
                        } 
                    ] 
                } 
            ] 
        }); 
  
        const BFS = []; 
  
        obj.eachBefore(d => BFS.push 
            ( 
                " ".repeat(d.depth)  
                    + `${d.depth}: ${d.data.name}` 
            )); 
  
        console.log(BFS); 
    </script> 
</body> 
  
</html> 