start on doc for javascript

docs/js/call.md

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+# Call a function
+
+The simplest way to get started in JavaScript with your micro:bit is to
+call one of the micro:bit's built-in JavaScript functions. Just like Blocks
+are organized into categories/drawers, the micro:bit functions are organized by
+namespaces.  The `basic` namespace contains a number of very helpful
+functions:
+
+```typescript
+basic.showString("Hello!")
+```
+
+If you want to see all functions available in a namespace, simply type `basic`
+followed by `.`; a list of all the functions will appear. 
+
+![](/static/mb/js/basicFun.png)
+
+Continue typing to select one of the functions, or click on one of the functions
+to select. You also narrow down the set of functions by typing, as below:
+
+![](/static/mb/js/basicIntell.png)
+
+# Function parameters
+
+You might have noticed that the call `showString` above takes one value, 
+the string to be scrolled on the LED screen. There is a second (optional)
+parameter that controls the speed of the the scroll. Try this:
+
+```typescript
+basic.showString("Hello!",50)
+```
+
+You might have noticed that the function list above shows all
+the available parameters for each function. 
+
+
+```typescript
+basic.showString("Hello!")
+basic.showLeds(`
+    . # . # .
+    . . . . .
+    . . # . .
+    # . . . #
+    . # # # .
+    `)
+basic.pause(1000)
+basic.clearScreen()
+basic.showString("Goodbye!")
+basic.showLeds(`
+    . # . # .
+    . . . . .
+    . . . . .
+    . # # # .
+    # . . . #
+    `)
+basic.pause(1000)
+basic.clearScreen()
+```