Package 'js'

Coffee Script

Description

Compiles coffee script into JavaScript.

Usage

coffee_compile(code, ...)

Arguments

code	a string with JavaScript code
...	additional options passed to the compiler

Examples

# Hello world
coffee_compile("square = (x) -> x * x")
coffee_compile("square = (x) -> x * x", bare = TRUE)

# Simple script
demo <- readLines(system.file("example/demo.coffee", package = "js"))
js <- coffee_compile(demo)
cat(js)
cat(uglify_optimize(js))

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JavaScrip Syntax Tree

Description

Esprima is a high performance, standard-compliant ECMAScript parser. It has full support for ECMAScript 2017 and returns a sensible syntax tree format as standardized by ESTree project.

Usage

esprima_tokenize(text, range = FALSE, loc = FALSE, comment = FALSE)

esprima_parse(text, jsx = FALSE, range = FALSE, loc = FALSE,
  tolerant = FALSE, tokens = FALSE, comment = FALSE)

Arguments

text	a character vector with JavaScript code
range	Annotate each token with its zero-based start and end location
loc	Annotate each token with its column and row-based location
comment	Include every line and block comment in the output
jsx	Support JSX syntax
tolerant	Tolerate a few cases of syntax errors
tokens	Collect every token

Details

The esprima_tokenize function returns a data frame with JavaScript tokens. The esprima_parse function returns the Syntax Tree in JSON format. This can be parsed to R using e.g. jsonlite::fromJSON.

References

Esprima documentation: http://esprima.readthedocs.io/en/4.0/.

Examples

code <- "function test(x, y){ x = x || 1; y = y || 1; return x*y;}"
esprima_tokenize(code)
esprima_parse(code)

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Evaluate JavaScript

Description

Evaluate a piece of JavaScript code in a disposable context.

Usage

js_eval(text)

Arguments

text	JavaScript code

Examples

# Stateless evaluation
js_eval("(function() {return 'foo'})()")

# Use V8 for stateful evaluation
ct <- V8::new_context()
ct$eval("var foo = 123")
ct$get("foo")

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Get the type of a JavaScript object

Description

JavaScript wrapper to typeof to test if a piece of JavaScript code is syntactically valid, and the type of object it evaluates to. Useful to verify that a piece of JavaScript code contains a proper function/object.

Usage

js_typeof(text)

Arguments

text	JavaScript code

Examples

js_typeof("function(x){return x+1}")
js_typeof("(function() {return 'foo'})()")
js_typeof("{foo : 123, bar : true}")

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Validate JavaScript

Description

Simple wrapper for ct$validate in V8. Tests if code constitutes a syntactically valid JS script.

Usage

js_validate_script(text, error = TRUE)

Arguments

text	character vector with JavaScript code
error	raise error on invalid code

Examples

js_validate_script("function foo(x){2*x}") #TRUE
js_validate_script("foo = function(x){2*x}") #TRUE

# Anonymous functions in global scope are invalid
js_validate_script("function(x){2*x}", error = FALSE) #FALSE

# Use ! or () to check anonymous function syntax
js_validate_script("!function(x){2*x}") #TRUE
js_validate_script("(function(x){2*x})") #TRUE

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Static analysis tool for JavaScript

Description

JSHint is a community-driven tool to detect errors and potential problems in JavaScript code. It is very flexible so you can easily adjust it to your particular coding guidelines and the environment you expect your code to execute in.

Usage

jshint(text, ..., globals = NULL)

Arguments

text	a string of JavaScript code
...	additional jshint configuration options
globals	a white list of global variables that are not formally defined in the source code

Value

a data frame where each row represents a jshint error or NULL if there were no errors

Examples

code = "var foo = 123"
jshint(code)
jshint(code, asi = TRUE)

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Compress and Reformat JavaScript Code

Description

UglifyJS is a JavaScript compressor/minifier written in JavaScript. It also contains tools that allow one to automate working with JavaScript code.

Usage

uglify_reformat(text, beautify = FALSE, ...)

uglify_optimize(text, ...)

uglify_files(files, ...)

Arguments

text	a character vector with JavaScript code
beautify	prettify (instead of minify) code
files	a character vector of filenames
...	additional arguments for the optimizer or generator.

References

UglifyJS2 Documentation: https://lisperator.net/uglifyjs/.

Examples

code <- "function test(x, y){ x = x || 1; y = y || 1; return x*y;}"
cat(uglify_optimize(code))
cat(uglify_reformat(code, beautify = TRUE, indent_level = 2))

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