jagdipa jagdipa - 6 months ago 7
JSON Question

Access JSON or JS property using string

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.

Answer

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';
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