V8

V8

Embedded JavaScript engine for R.

Basic Usage

library(V8)

# Create JavaScript context
ctx <- v8()

# Evaluate JavaScript
ctx$eval("var x = 1 + 1")
ctx$get("x")  # Returns 2

# Run multiple statements
ctx$eval("
  var a = 10;
  var b = 20;
  var sum = a + b;
")
ctx$get("sum")

Functions

# Define JavaScript function
ctx$eval("
  function add(a, b) {
    return a + b;
  }
")

# Call from R
ctx$call("add", 5, 3)

# With arrays
ctx$eval("
  function sum(arr) {
    return arr.reduce((a, b) => a + b, 0);
  }
")
ctx$call("sum", c(1, 2, 3, 4, 5))

Data Exchange

# R to JavaScript
ctx$assign("mydata", mtcars)
ctx$eval("console.log(mydata.length)")

# JavaScript to R
ctx$eval("var result = {a: 1, b: 2, c: [1,2,3]}")
ctx$get("result")

# JSON conversion
ctx$eval("var json = JSON.stringify({x: 1, y: 2})")
ctx$get("json")

Console Output

# Capture console.log
ctx$eval("console.log('Hello from JS')")

# Custom console
ctx$console(function(msg) {
  message("JS: ", msg)
})

Load JavaScript Libraries

# Load from file
ctx$source("library.js")

# Load from URL
ctx$source("https://cdn.example.com/library.js")

# Load bundled libraries
ctx$source(system.file("js/underscore.js", package = "V8"))

NPM Packages

# Use browserified npm packages
# First, bundle with browserify:
# browserify -r lodash -o lodash-bundle.js

ctx$source("lodash-bundle.js")
ctx$eval("var _ = require('lodash')")
ctx$call("_.chunk", c(1,2,3,4,5,6), 2)

Error Handling

# JavaScript errors become R errors
tryCatch({
  ctx$eval("throw new Error('Something went wrong')")
}, error = function(e) {
  message("JS Error: ", e$message)
})

# Syntax errors
tryCatch({
  ctx$eval("var x = ")
}, error = function(e) {
  message("Syntax error")
})

Multiple Contexts

# Isolated contexts
ctx1 <- v8()
ctx2 <- v8()

ctx1$eval("var x = 1")
ctx2$eval("var x = 2")

ctx1$get("x")  # 1
ctx2$get("x")  # 2

# Reset context
ctx1$reset()