Access JSON or JS property using string

Question

I have a JSON array like this:

_htaItems = [
    {"ID":1,
     "parentColumnSortID":"0",
     "description":"Precondition",
     "columnSortID":"1",
     "itemType":0},
    {"ID":2,
     "parentColumnSortID":"0",
     "description":"Precondition",
     "columnSortID":"1",
    "itemType":0}]

I want to update this by passing the ID, column name and new value to a function:

    function updateJSON(ID, columnName, newValue)
    {
        var i = 0;
        for (i = 0; i < _htaItems.length; i++)
        {
            if (_htaItems[i].ID == ID)
            {
                ?????
            }
        }
    }

My question is, how do I update the value? I know I can do something like the following:

 _htaItems[x].description = 'New Value'

But in my cause, the column name is being passed as a string.

possible duplicate of How to use a variable value for the key of another object? — Felix Kling
– Felix Kling, Commented Aug 11, 2011 at 13:58
@jagdipa Felix is right--no JSON here. You have an array built using the array literal syntax which contains objects that were built with the object literal syntax. — JAAulde
– JAAulde, Commented Aug 11, 2011 at 14:08
@Felix - this is a possible duplicate to sundry questions, but I couldn't quickly find one that used square bracket notation more than one level deep. — JAAulde
– JAAulde, Commented Aug 11, 2011 at 14:08

T.J. Crowder · Accepted Answer · 2011-08-11 14:01:19Z

32

In JavaScript, you can access an object property either with literal notation:

the.answer = 42;

Or with bracketed notation using a string for the property name:

the["answer"] = 42;

Those two statements do exactly the same thing, but in the case of the second one, since what goes in the brackets is a string, it can be any expression that resolves to a string (or can be coerced to one). So all of these do the same thing:

x = "answer";
the[x] = 42;

x = "ans";
y = "wer";
the[x + y] = 42;

function foo() {
    return "answer";
}
the[foo()] = 42;

...which is to set the answer property of the object the to 42.

So if description in your example can't be a literal because it's being passed to you from somewhere else, you can use bracketed notation:

s = "description";
_htaItems[x][s] = 'New Value';

answered Aug 11, 2011 at 14:01

T.J. Crowder

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3 Comments

Pedro Ferreira Over a year ago

What na elequent explanation ! I've read thousands of articles and could't get THE answer. Just save my day. Thank you!

u936293 Over a year ago

@T.J. Crowder: what if the referenced property is a string representing some arbitrary levels deep, eg "a.b[5].c", of an arbitrary object? Is there a smart way to avoid parsing the string into components and accessing each property one at a time?

T.J. Crowder Over a year ago

@OldGeezer - I'm afraid not. :-) Move in this question's answers: stackoverflow.com/questions/6491463/…

sternr · Accepted Answer · 2011-08-11 13:53:54Z

1

_htaItems[x][columnName] = 'New Value'; Or did I misunderstand you?

answered Aug 11, 2011 at 13:53

sternr

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1 Comment

sternr Over a year ago

To be fair, it's probably the time it took you to press the "code-style" button ;)

Digital Plane · Accepted Answer · 2011-08-11 13:54:04Z

0

Just do _htaItems[i][columnName] = newValue;. It will change the property specified in columnName to newValue.

answered Aug 11, 2011 at 13:54

Digital Plane

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Comments

JAAulde · Accepted Answer · 2011-08-11 14:08:40Z

0

You need to use square bracket notation, just like you did for array index:

_htaItems[i][columnName] = newValue;

edited Aug 11, 2011 at 14:08

answered Aug 11, 2011 at 13:53

JAAulde

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1 Comment

jagdipa Over a year ago

Well that was a embarassingly easy :D

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