Question

Say I have some HTML elements:

<div>First</div>
<div>Second</div>
<div>Third</div>

Whose content I select via a:

$('div').text();

How can I make a “foldl” operation on the elements (iterate, accumulating a result), for example to join them using a newline?

$('div').text().foldl('', function(){ ... join_or_whatever ... })

Answer 1

According to the Wikipedia article on folding, JavaScript’s Array.reduce() (for foldl) and Array.reduceRight() (for foldr) functions provide array folding.

So your specific task becomes:

var result = $.makeArray($('div')).reduce(function(prev,curr){ 
        return prev + '\n' + $(curr).text() 
});

Note that not all implementations of JavaScript support reduce and reduceRight, so see this example implementation if needed.

UPDATED: Since jQuery doesn’t return a true array for $(selector) and some platforms do not support reduce and reduceRight on jQuery’s “array-like” collection, I’ve updated the answer to use $.makeArray() as suggested below. Thanks to @royas for the catch.