Can't access array by named key in JavaScript

Question

I need to pass an array of objects to a php page as part of a larger data structure. I am trying to replicate this structure in JavaScript and pass it via json.

The arrays keys in php have been set as names which I require later in the process.

I know JavaScript doesn't use associated arrays and arrays in JavaScript are essentially objects but documentation suggests I should be able to use named keys.

If this is the case I should also be able to use variables as named keys by using a different syntax.

Can someone then please show me what I am doing wrong?

Example 1: numeric keys (works)

var dataTargets = [];
var obj = {
  'test': 'test'
};
dataTargets["0"] = obj;
alert(JSON.stringify(dataTargets));

Example 2: named keys (fails)

var dataTargets = [];
var obj = {
  'test': 'test'
};
dataTargets["test"] = obj;
alert(JSON.stringify(dataTargets));
//outputs []

Example 3: variable keys (fails)

var dataTargets = [];
var dtname = "test";
var obj = {
  'test': 'test'
};
dataTargets[dtname] = obj;
alert(JSON.stringify(dataTargets));
//outputs []

Is question why JSON.stringify() returns an array with out elements set? What is expected result? — guest271314
– guest271314, Commented Mar 7, 2017 at 2:50

gyre · Accepted Answer · 2017-03-07 02:51:45Z

4

The properties are actually being correctly assigned to each array; the problem is that JSON.stringify ignores all non-index properties of arrays (treating them more like lists and less like objects). If you want to use named keys in your objects, you will have to use plain objects {} rather than arrays []:

var alert = console.log.bind(console) // for demo purposes


// Example 1: numeric keys 

var  dataTargets = {};
var obj = {'test':'test'};
dataTargets["0"] = obj;
alert(JSON.stringify(dataTargets));


// Example 2: named keys

var  dataTargets = {};
var obj = {'test':'test'};
dataTargets["test"] = obj;
alert(JSON.stringify(dataTargets));


// Example 3: variable keys 

var  dataTargets = {};
var dtname = "test";
var obj = {'test':'test'};
dataTargets[dtname] = obj;
alert(JSON.stringify(dataTargets));
//outputs []

answered Mar 7, 2017 at 2:51

gyre

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1 Comment

user3846011 Over a year ago

Thankyou for this answer, it clarified both of the things I was trying to work out (was I assigning the value correctly or was JSON.stringify not accepting it due to the key not being numeric). For reference I am going to modify the object on the php page receiving the data to have an additional property rather than using the keys. Thanks again :-)

Zhis · Accepted Answer · 2017-03-07 03:09:50Z

0

what you did actually like this

example1:

var  dataTargets = [];
var obj = {'test':'test'};
dataTargets[0] = obj;
alert(JSON.stringify(dataTargets));
// outputs [{test:test}]

what you need is:

var  dataTargets = {};
var obj = {'test':'test'};
dataTargets["test"] = obj;
alert(JSON.stringify(dataTargets));
//{"test":{{test:test}}}

because array need to be access by index. And object can be what you need

answered Mar 7, 2017 at 3:09

Zhis

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Can't access array by named key in JavaScript

Example 1: numeric keys (works)

Example 2: named keys (fails)

Example 3: variable keys (fails)

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Example 1: numeric keys (works)

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Example 3: variable keys (fails)

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