Return values in multiple arrays

Question

My program is returning values in single array: ["addEcommerceItem", "hat", 29.99, "addEcommerceItem", "belt", 19.99];

I am trying to acheive (["addEcommerceItem", "hat", 29.99], ["addEcommerceItem", "belt", 19.99]);

Can anyone make suggestion

products = [
    ["hat", 29.99],
    ["belt", 19.99]
]

var testArray = new Array();

for(i in products){
    testArray.push('addEcommerceItem');
    testArray.push(products[i]);
}

var json = JSON.stringify(testArray);

<script type="text/javascript">
  var _paq = _paq || [];
  _paq.push(['trackPageView']);
  _paq.push(['enableLinkTracking']);
  _paq.push(json);
</script>

Answer 1

First of all, don't use for in enumerations on arrays.

Now, there are two ways of approaching the result you want. First, you can simply alter the existing array by prepending that item to every of them:

for (var i=0; i<products.length; i++)
    products[i].unshift("addEcommerceItem");

console.log(JSON.stringify(products));

If that's not what you want, you would construct a new array rather:

var _paq = […]; // somewhere

for (var i=0; i<products.length; i++)
    _paq.push(["addEcommerceItem"].concat(products[i]));

console.log(JSON.stringify(_paq));

Instead of the concat, you could of course use a second loop:

var _paq = […]; // somewhere

for (var i=0; i<products.length; i++) {
    var product = products[i],
        temp = [];
    temp.push("addEcommerceItem";
    for (var j=0; j<product.length; j++)
        temp.push(product[j]);
    _paq.push(temp); // push each array individually
}

console.log(JSON.stringify(_paq));

Answer 2

To achieve your desired output, I've modified the for-loop to splice in the additional value to the products array instead of pushing it to the testArray.

var testArray = new Array();

for (var i=0; i < products.length; i++){
    products[i].splice(0,0,'addEcommerceItem');
    testArray.push(products[i]);
}

A JS Bin demonstrating the results can be seen here.

Answer 3

Just write what you want to happen: replace each sub-array with its elements preprended by "addEcommerceItem". You could use concat for that:

function prepend(item) { return ["addEcommerceItem"] . concat(item); }

Or, if you prefer,

function prepend(item) { item.unshift("addEcommerceItem"); return item; }

Then it's just

function transform(products) { return products . map(prepend); }

Sample usage:

>> products = [ ["hat", 29.99], ["belt", 19.99] ]
>> transform(products)
<< [ ["addEcommerceItem","hat",29.99], ["addEcommerceItem","belt",19.99] ]

To call _paq.push with each item in the resulting array as one argument, then

_paq.push.apply(_paq, transform(products))

In ES6:

var prepend   = item     => ["addEcommerceItem", ...item];
var transform = products => products . map(prepend);

_paq.push(...transform(products));