Johnny Five, how to use a REPL
This post is part of the Johnny Five series. See the first post here.
When you run a program using Johnny Five, you can see that in the terminal, we have access to a REPL, a term that means Read-Evaluate-Print-Loop.
In other words, we can write commands in here.
Let’s try by creating a repl.js
file with this code:
const { Board } = require("johnny-five")
const board = new Board()
I am going to play with the LCD circuit made in the previous lesson.
Run the program with node repl.js
:
Next, we’re going to write some commands in the REPL.
Start by requiring the LCD class:
const { LCD } = require("johnny-five")
Then initialize an lcd
object from it:
const lcd = new LCD({ pins: [7, 8, 9, 10, 11, 12] })
Now write to the LCD display:
lcd.print("Hello!")
You’ll see a big message coming back:
Because the command returns a reference to the LCD object. This is to let us chain commands together, like this:
lcd.clear().print("Hello!")
If you don’t run clear()
, any new thing you write is going to be appended to the one already there.
To write to the second row, you call cursor(1)
(the default row is 0
:
lcd.clear().print("Hello from")
lcd.cursor(1, 0).print("Johnny-Five!")
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