What does the syntax d._children = d.children; stand for in d3.js?
d3.js, javascript
Solution
`_children` is just a temp variable that holds the children when they are hidden. When you click you are either taking `children` to null and storing the children in the temp variable, or, if `children` is already null, loading them from the temp variable.
Any temp variable could have been used. There is nothing special about `_children`. It is used to show an obvious relationship to `children`.
Problem
In various examples on tree visualizations such as this collapsible tree example the syntax `d._children = d.children;` is used. For example in this code block from the example above: ``` // Toggle children on click. function click(d) { if (d.children) { d._children = d.children; d.children = null; } else { d.children = d._children; d._children = null; } update(d); } ``` What does the syntax `d._children` exactly mean? To me it was not clear where this is defined and if it's d3.js specific or JavaScript syntax in general. Any tips on tree traversal tutorials which involve such schemes are more then welcome!