index.js
function keep(orig, dest, options) {
        var keep, i, t;
        keep = options.keep || [];
        if (keep.length === 0) {
            return dest;
        }
        for (i = 0; i < keep.length; i += 1) {
            t = orig[keep[i]];
            if (t !== undefined) {
                dest[keep[i]] = t;
            }
        }
        return dest;
    }
function keep(orig, dest, options) {
        var keep, i, t;
        keep = options.keep || [];
        if (keep.length === 0) {
            return dest;
        }
        for (i = 0; i < keep.length; i += 1) {
            t = orig[keep[i]];
            if (t !== undefined) {
                dest[keep[i]] = t;
            }
        }
        return dest;
    }
function keep ( orig , dest , options ) { var keep , i , t ; keep = options . keep || [ ] ; if ( keep . length === 0 ) { return dest ; } for ( i = 0 ; i < keep . length ; i += 1 ) { t = orig [ keep [ i ] ] ; if ( t !== undefined ) { dest [ keep [ i ] ] = t ; } } return dest ; }
Copy the 'options.keep' keys from orig to dest
Copy the options . keep keys from orig to dest