All combinations of at least two array elements

script

/**
 * Test to figure out combinations of at least two elements of provided array.
 *
 * by Sergei Sokolov, [email protected], 2015 April 27, St. Petersburg.
 * Fiddle: http://jsfiddle.net/sergiks/2ojgqxk1/
 */
function comb(a) {
    var l, cursor, mask, tail, out=[];
    l = a.length;
    if( l<2  ||  l>32) {
        console.error('Array should be at least 2, at max 32 elements. Provided is '+l+'-long. Fail.');
        return;
    }
    
	$('body').append( $('<div class="b-src">Source: [' + a.join(', ') + ']</div>'));

    for( cursor=0; cursor<l-1; cursor++) {	// cursor points to the first element of any combi
        tail = Math.pow( 2, l-cursor-1);	// 1 + max value of "the rest" after the cursor
        for( mask=1; mask<tail; mask++) {	// at least 1-bit-on mask to the tail: [01, 10, 11] for tail=4
	        				// mask indicates which additional elements to pick
	        				// mask to offset (cursor + 1)

            bit = 0x1;		// test each bit of mask, if
            combi = [ a[cursor]];
            for( b=0; b<tail; b++) {
                if( bit & mask) combi.push( a[ b+cursor+1]);
                bit = bit << 1;
            }
            out.push( combi);
            $('body').append( $('<div>' + combi.join(', ') + '</div>'));
        }
    }
    return out;
}

comb( [0,1,2,3]);