diff between array of text values and object keys

arrdiffobj.js

var inp = [ 'a', 'b', 'c', 'f', 'g' ]
    , out = [ 'd', 'e', 'c', 'b' ]
    , res = []
    ;

function diff(inp, out){
    var del = [], ign = [] , add = []
        , i, t1 = out.length, t2
        ;

    for ( i = 0; i < t1; i++ ) {
        if ( ( t2 = inp.indexOf(out[i]) ) === -1 ) {                                                                                                   
            del.push(out[i])
        } else {
            ign.push(out[i])
            inp.splice(t2,1)
        }
    }

    add = inp

    return [ del , ign , add ]
}

res = diff(inp, out)

console.log(res)
// res should be
// [
//   [ 'd', 'e' ]
// , [ 'b', 'c' ]
// , [ 'a', 'f', 'g' ]
// ]

out should probably be renamed current, as it is more descriptive of what it is.
t1 should be renamed closer to what it is.
I'd pull setting t2 out of inside the if and make it it's own statement. also, probably rename it to item or something.
instead of splicing input, i'd just push it into add instead, that way you don't mutate the input variable, though, that will require a bit more logic. It's a trade off.
out[i] should probably be pulled out to a temp variable as well since it's being used in several places.
returning a new array could be a performance issue.