Uncaught TypeError: Cannot read property 'doThings' of undefined

Question

I have an array of nodes that will beautifully be populated with objs

var nodesArray = [];

var obj = function(nodeSpan){
    this.nodeS = nodeSpan;

    this.doThings = function(){
            console.log(this.nodeS);
    };
}

I put lots of obj's into nodeArray

var newObj = new obj(thisIsASpan) ///trust me that's a span
nodesArray.push(newObj);
//etc

I call a map function on each node adding an event listener.

Array.prototype.map.call(nodesArray, function(obj, index) {
        obj.nodeS.addEventListener('click', function(obj, index) {
                nodesArray[index].doThings(); ////Throws error in title.
        });
});

I click on one of the damn spans.

I get error in title, I then walk to break room, I then have breakdown.

I would start by console.loging out the nodesArray and then see if it is working the same way you think it is .. then console.log index and obj out — jdave, Oct 06 '16 at 20:04
@jdave the index was correctly passed to the `addEventListener` — christopher clark, Oct 06 '16 at 20:05
BTW, you don't need to use `Array.prototype.map.call` when your variable contains a real array. Just use `nodesArray.map(...)`. The complex syntax is only needed for array-like objects. — Barmar, Oct 06 '16 at 20:17

epascarello · Accepted Answer · 2016-10-06T20:11:49.483

3

You should not be adding obj and index when you are defining the click, those are being set when the click is being fired. In your case the first argument is the event object and the second is undefined since click only has one argument.

Array.prototype.map.call(nodesArray, function(obj, index) {
        obj.nodeS.addEventListener('click', function(event) {
                nodesArray[index].doThings(); 
        });
});

edited Oct 06 '16 at 20:11

answered Oct 06 '16 at 20:07

epascarello

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I hug @epascarello – christopher clark Oct 06 '16 at 20:10
But seriously, why does addEventListener have access to the index then? And why wouldn't I be able to pass index explicitly? – christopher clark Oct 06 '16 at 20:11
because the variables are in same block scope. – epascarello Oct 06 '16 at 20:12

Uncaught TypeError: Cannot read property 'doThings' of undefined

1 Answers1