How do you make a level editor

How do you make a level editor where you can make your own levels something kinda simple that has the basic stuff

this.y=mouseY
this.x=mouseX

put that on drag and drop and put it a hitbox

First off you need a program (game?) able to load levels from external files.
If you did not made that program you need to know what kind of structure those level files use.
For the editor you have to provide all the graphic and logic elements that could make a level.
Provide the ability to arrange them (usually drag and drop)
Record on a file all the types and position
Provide a way to save the file

I have a game made but I think I’ll need help with making the level editor because I don’t really know javascript well I know easy stuff like variables prompts and alerts but none of those are really helpful

@blurredPixels I think I have an idea I was experimenting with the drawing code and I made it so it will clone a square with the hitbox so it would be like a wall but idk how to make it so it clones something else like if you change it to a circle idk how to do that