Question

I’m trying to merge array of JSON objects to one object using jQuery.extend function.
Assume, i have a sample array:

arr = [{a:4},{b:5}];

in case:

arr.reduce( $.extend  ) 
//result { "1":{b:5}, a:4, b:5 }

but

arr.reduce( function( a, b){ return $.extend(a,b) } );
//is ok: { a:4, b:5 }

why?

Answer 1

The function passed to reduce will receive four arguments (the last two are the index of the current item and the array that reduce was called on). You’re only interested in the first two, but jQuery.extend takes a variable number of arguments, so it slurps them all up. By explicitly writing a function that takes two arguments and passes them to extend, you avoid this and get the behavior you expected.