Question

Ok, so this shouldn t be difficult, however I have encountered weird and bizarra flukes.

I am trying to pack a tree into an array, where each node is something like:

title: string-for-display
key: id-value
children: array of child nodes

the fluke is so strange I can t comprehend it at all: when I try to add a child to a node, I do something like

if(node.children == undefined) {
  node.children = new Array();
}

node.children.push({ title: value, key: key });

this was deleting some previously inserted nodes....so I did some debugging and found that this code:

if(node.children == undefined) {
  node.children = new Array();
}

was at fault, which doesn t make any sense at all - node.children = new Array() shouldn t delete ANYTHING if node.children is undefined......, right?

Am I doing something wrong? if so, how do I pack the tree into an array in Javascript?

Answer 1

The way you are using the undefined value is not consistent with Javascript standard practices. I m not sure if this will solve your problem, but try changing you code to

if (typeof(node.children) ==  undefined ) { 
  node.children = [];
}

This might actually help. Also, as you can see, using the Array constructor is unnecessary: [] creates a new empty array.

Undefined is not an actual reserved word in Javascript. There is nothing preventing you from setting

undefined = 2;

after which any comparisons to it will behave unpredictably.

Answer 2

Have you tried the in operator?

if (!("children" in node))
  node.children = [];

Answer 3

To check if a property exists on an object, use hasOwnProperty

if (!node.hasOwnProperty( children )) {
    node.children = [];
}

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