Using string from variable as property name for JSON in Javascript?

Question

So I'm grabbing a JSON via AJAX, but need to re-configure it. Part of that means using a string contained in a variable as the property name of a nested object.

But Javascript doesn't allow this. It treats variables as literal strings, instead of reading the value.

Here's a snippet:

var pvm.exerciseList = [];

$.get('folder_get.php', function(data){
    var theList = $.parseJSON(data);
    $.each(theList, function(parentFolder, files) {
        var fileList = [];
        $.each(files, function(url, name) {
            thisGuy.push({fileURL: url, fileName: name});
        });
        pvm.exerciseList.push({parentFolder: fileList});
    });
});

Is there anyway around this? I need to extract the string contained in "parentFolder." Right now, JS is just interpreting it literally.

Does this answer your question? Dynamically access object property using variable — Heretic Monkey
– Heretic Monkey, Commented Jul 11, 2022 at 15:37

Michael Berkowski · Accepted Answer · 2012-03-08 04:02:38Z

9

Use the [] syntax to resolve a variable as a property name. This might require an intermediary {}:

$.get('folder_get.php', function(data){
    var theList = $.parseJSON(data);
    $.each(theList, function(parentFolder, files) {
        var fileList = [];
        $.each(files, function(url, name) {
            thisGuy.push({fileURL: url, fileName: name});
        });

        // Make an object    
        var tmpObj = {};
        // And give it a property with the current value of parentFolder
        tmpObj[parentFolder] = fileList;
        // Then push it onto the array
        pvm.exerciseList.push(tmpObj);
    });
});

answered Mar 8, 2012 at 4:02

Michael Berkowski

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3 Comments

Benjamin Allison Over a year ago

Awesome! Thanks so much. Javascript has little "gotchas" hiding around every corner.

Michael Berkowski Over a year ago

@BenjaminAllison It's a very flexible and nuanced language, worth learning in detail. Not that you asked, but I recommend reading Douglas Crockfor's JavaScript: The good parts to get a handle on where the language's dark alleys and bright spots lie.

Benjamin Allison Over a year ago

I've read it about 3 times, and will probably read it another 20 times!!! Thanks again Michael.

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