Concat JSON array objects without index 0 undefined

Question

This is a basic question but I'm just curious about an elegant way to do something (I already have solution for dirty way). I have the code below to start with empty var a as JSON array. Then I want to concat more JSON objects array into it later on:

var a = [{}];
a = a.concat([{"a":"b1"},{"a":"b2"}]);
a.splice(0,1); // This does not work to remove index 0 of undefined
console.log(a[0].a + " " + a[1].a + " " + a[2].a);

The problem is when a declared, it already came with undefined in index 0. I could re-generate the whole array to remove all undefined using push.apply() but that seems unnecessary overhead. See:

Javascript: How to remove an array item(JSON object) based on the item property value?

Two questions:

Is there a way to concat arrays but override the index 0 on initial concat?
OR is there a way to use concat without declaring it a = [{}]?

There's really no such thing as a "JSON array" in JavaScript. It's just an array. — Pointy
– Pointy, Commented May 21, 2013 at 20:26
Also your array "a" does not have undefined in index 0; it has an empty object. If you declare the array with just [], then it will have a length of 0. — Pointy
– Pointy, Commented May 21, 2013 at 20:27
Are you aware your error comes from a[2].a at the console.log line? At that point, there's not a[2]. Before the console.log call, there's no error. — bfavaretto
– bfavaretto, Commented May 21, 2013 at 20:28

epascarello · Accepted Answer · 2013-05-21 20:27:04Z

5

You should just be declaring it as an empty array, there is no need for the empty object inside.

var a = [];

Output in a console

> var a = [];
  undefined
> a = a.concat([{"a":"b1"},{"a":"b2"}]);
  [Object, Object]

answered May 21, 2013 at 20:27

epascarello

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