Assign values to an array within an array

Question

The data structure for my project is supposed to look like:

{
"result":"ok",
"content":[
    {
        "type":"1d",
        "lower":1359129600,
        "upper":1359133200,
        "mean":29.071428571428573

    },{
        "type":"1d",
        "lower":1359133200,
        "upper":1359136800,
        "mean":27.232142857142858
    }]
}

I am trying to assign values for lower, upper, mean.

var dataResult = {result:"ok", content:[{type:"1d", lower:"", upper:"", mean:""}]};
var scope = this;
  $.ajax({
    type: "POST",
    async: true,
    url: scope.fetchUrl,
    data: { query: dataQuery }
    })
    .done(function( data ) {
      for(var i = 0; i < data["reading_list"].length; i++){
        dataResult.content[i].lower = convertToUnix(data["reading_list"][i]["ts"]);
      }

I keep getting "Uncaught TypeError: Cannot set property 'lower' of undefined" and I'm don't know where I'm going wrong. Any help would be appreciated

The error means that dataResult.content[i] returns undefined. You cannot set a property on undefined. Simple test: var foo; foo.bar = 42;. Why is it undefined? Because the value of i is not a property of dataResult.content. — Felix Kling
– Felix Kling, Commented Feb 18, 2015 at 20:41

Pointy · Accepted Answer · 2015-02-18 20:36:49Z

1

Your "content" array starts off with just one object in it. If your ajax result has more than that, then those array entries will be undefined.

Before trying to do the assignment, just make sure the array element has an object in it:

    if (!dataResult.content[i])
      dataResult.content[i] = {};
    dataResult.content[i].lower = convertToUnix(data["reading_list"][i]["ts"]);

answered Feb 18, 2015 at 20:36

Pointy

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3 Comments

user2100620 Over a year ago

The error is no longer there but when I console.log dataResult.content.lower to see the output, it shows undefined.

Pointy Over a year ago

@user2100620 well dataResult.content is the whole array itself; you need to log the whole array or else individual elements of the array. The array doesn't have a "lower" property, but the individual elements do.

user2100620 Over a year ago

Thank you! This all makes a lot more sense now

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