index.js
function addChild(parent, child) {
        parent._children.push(child)
        incChildrenVersion(parent)
        return parent
    }
function addChild(parent, child) {
        parent._children.push(child)
        incChildrenVersion(parent)
        return parent
    }
function addChild ( parent , child ) { parent . _children . push ( child ) incChildrenVersion ( parent ) return parent }
add child to pnode
add child to pnode