Hi, I just finisehd the example „Active learning: Working through a JSON example“ .
When I open the console I get the following error-message:
“heroes.html:54 Uncaught TypeError: Cannot read property ‘length’ of undefined
at showHeroes (heroes.html:54)
at XMLHttpRequest.request.onload (heroes.html:38)”
I already started to replace the mentioned lines with the code form the “heroes-finished.html” . I even tried to replace the whole function, but it is still not working.
What else would you recommend to find the bug ?
Thanks for help,
Raphael
Hi @r.p.e.arw, I’d be happy to try and figure it out. Can you post a copy of the JS source code as you had it when you were getting the error?
Hi @chrisdavidmills, that’s nice of you. Here the code:
<title>Our superheroes</title>
<link href="https://fonts.googleapis.com/css?family=Faster+One" rel="stylesheet">
<link rel="stylesheet" href="style.css">
<header>
</header>
<section>
</section>
<script>
var header = document.querySelector('header');
var section = document.querySelector('section');
var requestURL = 'https://mdn.github.io/learning-area/javascript/oojs/json/superheroes.json';
var request = new XMLHttpRequest();
request.open('GET', requestURL);
request.responseText = 'json';
request.send();
request.onload = function() {
var superHeroes = request.response;
populateHeader(superHeroes);
showHeroes(superHeroes);
}
function populateHeader(jsonObj) {
var myH1 = document.createElement('h1');
myH1.textContent = jsonObj['squadName'];
header.appendChild(myH1);
var myPara = document.createElement('p');
myPara.textContent = 'Hometown: ' + jsonObj['homeTown'] + ' // Formed: ' + jsonObj['formed'];
header.appendChild(myPara);
}
function showHeroes(jsonObj) {
var heroes = jsonObj['members'];
for(var i = 0; i < heroes.length; i++) {
var myArticle = document.createElement('article');
var myH2 = document.createElement('h2');
var myPara1 = document.createElement('p');
var myPara2 = document.createElement('p');
var myPara3 = document.createElement('p');
var myList = document.createElement('ul');
myH2.textContent = heroes[i].name;
myPara1.textContent = 'Secret identity: ' + heroes[i].secretIdentity;
myPara2.textContent = 'Age: ' + heroes[i].age;
myPara3.textContent = 'Superpowers:';
var superPowers = heroes[i].powers;
for (var j = 0; j < superPowers.length; j++) {
var listItem = document.createElement('li');
listItem.textContent = superPowers[j];
myList.appendChild(listItem);
}
myArticle.appendChild(myH2);
myArticle.appendChild(myPara1);
myArticle.appendChild(myPara2);
myArticle.appendChild(myPara3);
myArticle.appendChild(myList);
section.appendChild(myArticle);
}
}
</script>
This line is the problem. It should be
request.responseType = 'json';
As it was, the object was being returned as a text string, not a json object, so none of the values could be read out of it.