pxt-calliope/docs/reference/input/on-button-pressed.md
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Co-authored-by: Juri <gitkraken@juriwolf.de>
2020-09-08 02:04:25 -07:00

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# On Button Pressed
Start an [event handler](/reference/event-handler) (part of the program that will run when something happens, like when a button is pressed).
This handler works when button `A` or `B` is pressed, or `A` and `B` together.
When you are using this function in a web browser, click the buttons on the screen instead of the ones
on the @boardname@.
* For button `A` or `B`: This handler works when the button is pushed down and released within 1 second.
* For `A` and `B` together: This handler works when `A` and `B` are both pushed down, then one of them is released within 1.5 seconds of pushing down the second button.
```sig
input.onButtonPressed(Button.A, () => {})
```
Find out how buttons provide input to the @boardname@ in this video:
https://www.youtube.com/watch?v=t_Qujjd_38o
## Example: count button clicks
This example counts how many times you press the `A` button.
Each time you press the button, the [LED screen](/device/screen) shows the `count` variable getting bigger.
```blocks
let count = 0
basic.showNumber(count)
input.onButtonPressed(Button.A, () => {
count++;
basic.showNumber(count);
})
```
## Example: roll dice
This example shows a number from 1 to 6 when you press the `B` button.
```blocks
input.onButtonPressed(Button.B, () => {
let dice = randint(0, 5) + 1
basic.showNumber(dice)
})
```
## ~hint
This program adds a `1` to `random(5)` so the numbers on the dice will come out right.
Otherwise, sometimes they would show a `0`.
## ~
## See also
[button is pressed](/reference/input/button-is-pressed), [forever](/reference/basic/forever), [random](/blocks/math)