Setting JSON key with indexed array value

Question

I am trying to populate a JSON object by automatically setting the keys for an JSON object based on the string value of another array. For example,

var test = ["a","b"]
{test[0]:"A"}

However, I get a Syntax error when I do this, if I manually set the value as the string as shown in the third line {"a":"A"} this issue does not happen. I've checked that test[0] does indeed print out "a" and its datatype is a string. Is there any reason why this might be happening?

`{[test[0]]:"A"}` results in `{a: "a"}` - surround your key in brackets, else its trying to write the key as `test[0]` — tymeJV, Jun 01 '18 at 16:11
[There is no such thing as a "JSON Object"](http://benalman.com/news/2010/03/theres-no-such-thing-as-a-json/) ... what you have is an object literal. That has nothing to do with JSON. — Felix Kling, Jun 01 '18 at 16:12
you are looking for [computed property names](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Object_initializer#Computed_property_names). — Nina Scholz, Jun 01 '18 at 16:12
*"Is there any reason why this might be happening?"* Yes, `x[y]` is simply not valid syntax in place of the key in an object literal. — Felix Kling, Jun 01 '18 at 16:15

score 2 · Accepted Answer · answered Jun 01 '18 at 16:11

2

Try the following:

    var test = ["a","b"]
    var obj = {
        [test[0]]:"A"
    };
    console.log(obj);

answered Jun 01 '18 at 16:11

amrender singh

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Thanks, this solution works, could you explain why the brackets around test[0] is necessary in this case? – ROBOTPWNS Jun 01 '18 at 16:15
It is used for computed property names . For reference : https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Object_initializer#Computed_property_names – amrender singh Jun 01 '18 at 16:23

Setting JSON key with indexed array value

1 Answers1