CODEWITHSUNDEEP
javascriptxml
user8313545
user8313545

Reputation:

(infinite?) loop in javascript code

I have the following JavaScript code to "display" XML on a website:

function createChild(node,tabindex){

    var child = node.childNodes;

    var r = '';

    var tabs = '';

    for(i=0;i<tabindex;i++){

        tabs += "\t";

    };

    for(i=0;i<child.length;i++){

        if(child[i].nodeType == 1){

            r += tabs+"&lt;"+child[i].nodeName+"&gt;\n";

            if(child[i].hasChildNodes()){ r += createChild(child[i],1); }; // here is where it fails!

            r += tabs+"&lt;/"+child[i].nodeName+"&gt;\n";

        }

    }

    return r;

 };


function parseXML(xml){

    var doc = new DOMParser().parseFromString(xml,'application/xml');

    var node = doc.getElementsByTagName('*')[0];

    var r = '';

    r += "&lt;<span class=\"highlight highlight-blue\">"+node.nodeName+"</span>&gt;\n";

    if(node.hasChildNodes()){ r += createChild(node,1); };

    r += "&lt;<span class=\"highlight highlight-blue\">/"+node.nodeName+"</span>&gt;\n";

    $('.viewer').html(r);
};

This works fine on XML like this:

<properties>
    <property></property>
</properties>

But it fails to work when there is more than one child like this:

<properties>
    <property>
        <value></value>
    </property>
</properties>

The code keeps running until my browser crashes. I think there is an infinite loop in it, but I'm not sure. Does anyone have a tip for me?

Upvotes: 0

Views: 94

Answers (1)

PeterMader
PeterMader

Reputation: 7285

This is why you should always declare your variables:

// declare 'i'
for(var i = 0; i < tabindex ; i++){
  tabs += "\t";
};

If you don't declare i in the function scope, it will be global, thus interfering with the for loop in a recursive function call:

  1. The i variable is set to 0 in the first function call.

  2. The function is calls itself.

  3. The i variable is set to 0.

  4. The function returns.

  5. i is now 0 again, so the loop in the first frame will run forever.

So somewhere in the createChild function, you have to declare i, either before the first loop or in the first loop. You can also use let.

Upvotes: 3

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