Select Next Keyframe (in selected property) script

Question

I find myself constantly crafting individual keyframes manually, so being able to automatically select the next/previous keyframe on a selected property with a shortcut (assigned to a script, since there's no such functionality in After Effects, being "Select Previous/Next Keyframes" the closest thing) instead of locating the keyframe and clicking on it, would save me, and everyone, hours of pointing and clicking.
After some research I thought It was not possible but after some more (looking at scripts like this AE ENHANCERS • View topic - Exponential Scaling and Re: How can I access the layer keyframes?) , I've started to wonder if it is scriptable.
Hope it is clear what I'm trying to achieve;
Basically I'd like that pressing Shift+K would take me to the next keyframe in the selected property AND select it (Shift+J for the previous one) and
pressing Ctrl+Shift+K would select the next keyframe in the selected property without actually moving the Current Time Indicator (Ctrl+Shift+J for the previous one).
(I think it makes sense and it is consistent with the almighty J and K shortcuts but I didn't know how to write the code or ask for this functionality. Haven't been lucky asking to fellow animators either).
Thanks,
Oliver

Answer 1

Here here!
SelectJumpNextKey:
In a selected keyframe/keyframes, will select the next one in time AND jump the CTI to the time of that keyframe or, if multiple selected, the last of the selected keyframes.
(If you don't want the time jump but only the selection, just remove the second $.global.script_doJumpToLastSelectedKey script).
$.global.script_doSelectNextKeys || (script_doSelectNextKeys = function script_doSelectNextKeys(){  
    var comp = app.project.activeItem, props, n, p, idx, max=-Infinity;  
    if (comp instanceof CompItem){  
        props = comp.selectedProperties;  
        for (n=0; n<props.length; n++){  
            p = props[n];
            if (p.numKeys && p.selectedKeys.length>0){
                // get index of the last selected key
                idx = p.selectedKeys[p.selectedKeys.length-1];
                // change to next key
                if (idx<p.numKeys) ++idx;
                // select only that key
                p.selected = false;
                p.setSelectedAtKey(idx, true);
                // update the time
                max=Math.max(max, p.keyTime(idx));
         // this sets the composition time (CTI) to max
         if (-Infinity<max) comp.time = max;
    return
script_doSelectNextKeys();
$.global.script_doJumpToLastSelectedKey || (script_doJumpToLastSelectedKey = function script_doJumpToLastSelectedKey(){   
    var comp = app.project.activeItem, props, n, p, max=-Infinity;   
    if (comp instanceof CompItem){   
        props = comp.selectedProperties;   
        for (n=0; n<props.length; n++){   
            p = props[n]; 
            if (p.numKeys && p.selectedKeys.length>0) max=Math.max(max, p.keyTime(p.selectedKeys[p.selectedKeys.length-1])); 
        if (-Infinity<max) comp.time = max; 
    return;   
script_doJumpToLastSelectedKey();
And this (nevermind the more than possible coding aberrations on my part) is what I originally aimed for. I think that not only it is simply amazing ("It just works") but so intuitive (specially using Shift+J/K) that should be an After Effects default.
Your version (select keyframes under current time in the selected properties) is super great too, but it serves a whole different purpose.
Now, for the SelectJumpPrevKey, I just have to figure how to make this bit:
$.global.script_doJumpToFirstSelectedKey || (script_doJumpToFirstSelectedKey = function script_doJumpToFirstSelectedKey(){   
    var comp = app.project.activeItem, props, n, p, max=-Infinity;   
    if (comp instanceof CompItem){   
        props = comp.selectedProperties;   
        for (n=0; n<props.length; n++){   
            p = props[n]; 
            if (p.numKeys && p.selectedKeys.length>0) max=Math.max(max, p.keyTime(p.selectedKeys[p.selectedKeys.length-1])); 
        if (-Infinity<max) comp.time = max; 
    return;   
script_doJumpToFirstSelectedKey();
actually go to the first keyframe selected and not the last (which, as simple as it may seem, to me is like watching the Matrix code and pushing random buttons in russian to see what happens).
Sorry I couldn't make your last code work and insted just stitched to scripts together! for some reason, the CTI wasn't jumping.
Mega thanks!!
Oliver