An event in computer science is an action or occurrence that is detected by a computer. For example, when someone clicks the button on their mouse, it generates a “mouse click event” for the computer. In real life, there are also events that might be associated with an action, like cause and effect. Here are some examples:

Event Action
It starts raining People open umbrellas
The bell rings Students go to class
The power button is pressed The computer turns on
The mouse button is clicked An application opens

Can you think of some other events and what they might cause to happen?

In programming, an event handler is a part of your program that runs when a specific event happens (it “handles” the event). In MakeCode, an event handler block looks like a square with a gap in the middle and usually starts with the word “on”:

player.onTravelled(TravelMethod.Walk, function () {

blocks.onBlockPlaced(blocks.block(Block.Grass), function () {

mobs.onMobKilled(mobs.animal(AnimalMob.Chicken), function () {

player.onChat("jump", function () {