JSON.stringify无法正确转换array.object

Question

I'm having a problem with JSON.stringify

I'm trying to pull all the meta tags out of the page and pass them to a firefox worker file to work through them and to return back an object.

So my code previously worked when I didn't have a worker running the issue has only cropped up when I have moved to using worker file (for reasons I can't go into I need to use a worker!)

So previously I would get all the meta tags using

var metas = document.getElementsByTagName("meta");

then I could loop through the metas object by using

for (var index in metas){
  var currentMeta = metas[index];
//(and so on, this code worked perfectly)

The problem occurs when I move to the external worker file scenario. What happens is I pull the meta tags out as normal, and then I use JSON.stringify to something that I can push to the worker.

After all that intro blab, here is the root of my problem: Take for example that I land on a page with the following code within the html

<meta content="width=1024" name="viewport">
<meta charset="UTF-8">
<meta content="Mozilla Hacks – the Web developer blog" name="title">

If I run the following code I get an array

var metas = document.getElementsByTagName("meta");

returns an array 3 elements

[meta, meta, meta]

If I stringify it using:

var jsonMetas = JSON.stringify(metas);

I would expect to jsonMetas to hold something like:

{"0":{"content":"width=1024","name":"viewport"},"1":{"charset":"UTF-8"},"2":{"content":"Mozilla Hacks - the web developer blog","name":"title"} }

However when I look at the jsonMetas object I see this returned:

{"0":{"constructor":{}},"1":{"constructor":{}},"2":{"constructor":{}}}

Huh?????

I'm not that good at JavaScript, so could you please explaining (in very small words :) ) what is going on?

Why does the stringify call return the unusually structured object? What am I doing wrong?

Thanks in advance for your answers.

Answer 1

You could use the following :

var metas = document.getElementsByTagName("meta");
var arr = [];
for (var i = 0; i < metas.length; i++) {
    var obj = {};
    for (var j = 0; j < metas[i].attributes.length; j++) {
        var att = metas[i].attributes[j];
        obj[att.name] = att.value;
    }
    arr.push(obj);
}

var jsonMetas = JSON.stringify(arr);
console.log(jsonMetas);​

results in:

[
    {
        "http-equiv": "content-type",
        "content": "text/html; charset=UTF-8"
    },
    {
        "content": "width=1024",
        "name": "viewport"
    },
    {
        "charset": "UTF-8"
    },
    {
        "content": "Mozilla Hacks – the Web developer blog",
        "name": "title"
    }
]

Answer 2

The reason is that document.getElementsByTagName doesn't return JSON, it returns XML. So, you'd need to use something like this to get your desired output:

var jsonMetas = [];
for (i=0 ; i<metas.length ; i++) {
    var thisMeta = {};
    for (j=0 ; j<metas[i].attributes.length ; j++) {
        thisMeta[metas[i].attributes[j].name] = metas[i].attributes[j].value;
    }
    jsonMetas.push(thisMeta);
}

Output of JSON.stringify(jsonMetas) for this page:

"[{"name":"relativepagescore","content":"0"},{"name":"title","content":"javascript - JSON.stringify not converting array.object correctly - Stack Overflow"}]"