pxt-calliope/docs/blocks/on-start.md

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# On Start
An event that runs when the program starts.
The ``on start`` is a special event that runs when the program starts, before any other event.
Use this event to initialize your program.
## Example
In this example, ``on start`` sets a dimmer brightness on the screen and the button handler shows a string.
```blocks
input.onButtonPressed(Button.A, () => {
basic.showString("Hello!")
})
led.setBrightness(50)
```
## What about JavaScript?
``on-start`` only exists in the block editor. In JavaScript, all code executes sequentially from the first line.