Make a Platformer With Coyote Time and Jump Buffering

What you will build

Reach one beacon across three static platforms.

1. Extract into a new folder and run node check.mjs from that folder.
2. For the browser games, run python3 -m http.server 8080 with Python 3 and open http://localhost:8080/index.html. Do not open modules with file://.
3. Read the full setup instructions and the original code licence. Keep your existing game on a separate test branch.

The JavaScript behaviour checks and native C comparison can run independently of the browser. Ghidra UI, physical-phone and your engine integration are separate checks. This is a small reference, not a certification of your project.

Explore the related game idea · Start with Build a Game · Improve your existing game

Five practical steps

1. Run the geometric room

   Choose Platformer in the workshop and Start. Move with arrows or A/D; Jump or Space is a press. Inspect platformer.mjs: positions are pixels, gravity is pixels per second squared, and updates run at a fixed 60Hz.

   Expected result: A player rests on the first platform without drifting.

   Check it: Release all controls and confirm the player remains on top of the floor.

   stepObserve the inputs → check the state → compare the result

2. Solve landings from the previous bottom

   Store the previous bottom edge, then apply gravity and movement. A landing needs downward velocity, a crossing of the platform top and horizontal overlap. Testing only current overlap may let a falling character pass through a thin platform.

   Expected result: The player lands on each platform while falling.

   Check it: Jump through a platform from below; it acts as a one-way platform, not a ceiling.

3. Add short grace windows

   Coyote time allows a jump briefly after leaving a ledge; a buffer remembers a recent jump press until a landing. Both last 0.1–0.12 seconds in this example. Consume both when a jump is accepted so a held button cannot grant repeated jumps.

   Expected result: A slightly late or early press can still jump once.

   Check it: Compare a press 0.05 seconds after walking off with a press after 0.2 seconds.

4. Add a clear endpoint and reset

   Reach the green beacon on the top platform to win. Falling below the room resets player state. A won state freezes simulation while restart reconstructs a fresh state. Use a checkpoint later rather than hiding a broken level behind generous grace time.

   Expected result: A short route with a reachable end and reliable restart.

   Check it: Complete the route, wait, restart twice and fall intentionally; no old vertical speed or buffer survives.

5. Build one upgrade

   Start with the supplied complete source and shared lab runner, then add one moving hazard or checkpoint. Keep one-way landing rules in mind. A full platformer also needs side collisions, slopes, camera, animation and level tools; add them in separate milestones.

   Expected result: An original small game with one tested extension.

   Check it: Repeat keyboard/touch, pause/resume and the entire route after your change.

Read and reuse the actual code

platformer.mjs: complete source · Standalone behavioural checks · Shared browser runner and input. Original BINX Forge code, MIT; the package includes every required file and its notice.

export function create(){return {x:24,y:260,vy:0,grounded:true,coyote:.1,buffer:0,coins:0,won:false};}
export const platforms=[{x:0,y:280,w:150},{x:195,y:230,w:110},{x:360,y:180,w:180}];
export function step(s,i,dt){
 if(s.won)return;
 s.buffer=i.action?.12:Math.max(0,s.buffer-dt);s.coyote=s.grounded?.1:Math.max(0,s.coyote-dt);
 if(s.buffer>0&&s.coyote>0){s.vy=-350;s.buffer=0;s.coyote=0;s.grounded=false;}
 const oldBottom=s.y+20;s.x=Math.max(0,Math.min(620,s.x+(Number(!!i.right)-Number(!!i.left))*180*dt));
 s.vy+=900*dt;s.y+=s.vy*dt;s.grounded=false;
 for(const p of platforms)if(s.vy>=0&&oldBottom<=p.y&&s.y+20>=p.y&&s.x+20>p.x&&s.x<p.x+p.w){s.y=p.y-20;s.vy=0;s.grounded=true;break;}
 if(s.y>360)Object.assign(s,create());
 if(s.x>495&&s.y<180){s.coins=1;s.won=true;}
}

Code rights: the included MIT notice permits use, modification and distribution, including commercial games and source products, with the copyright and licence notice. Added third-party files have their own terms. Read the official licence & usage terms.

Common failures and fixes

Make Your Game Better

Change one system after the baseline works. Keep the free reference and compare the same inputs before and after.

Optional building blocks from original creators

ScreenshotFree

Godot Engine contributors · Original screenshot ↗ · CC BY 4.0 ↗. Resized and compressed.

Godot Engine contributors

Godot

Free, open-source game editor for 2D and 3D projects, with scene, animation and interface tools.

MITEngine

Official licence ↗Licensing summary, not legal advice. Check the exact edition and use.

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Creator previewFree

Kenney

UI Pack

Interface artwork for buttons, panels and sliders.

CC0-1.0Asset pack

Official licence ↗Licensing summary, not legal advice. Check the exact edition and use.

See previews & details

Inspect exact formats and editions on each resource page. Pay for a resource only when it fills an identified gap; the free code exercise needs no paid engine or pack.

Licensing summary, not legal advice. Before publishing or selling, check exact terms for finished-game use, reselling files and including files in a source/template product separately.

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