JSure: The Javascript Checker

Jsure

Description

Jsure is a "lint" for Javascript, which is also known as Ecmascript. It checks syntax and a little bit of semantics.

Usage

You run jsure on your source files and jsure spits out ANSI-colored warnings and errors with excerpts from your code on your terminal.

  jsure [options] file_1.js file_2.js ... file_n.js

This is equivalent to

  cat file_1.js ... file_n.js > file.js
  jsure [options] file.js

except for the reported error locations.

Actions

jsure will read and parse the input files. If there is any unparseable file, it will report an error and stop. By default, Jsure will only check the syntax. For more advanced checking, you must use on or more of the following options:

-check: The most useful, all-purpose check (unused vars, etc.)
-forbidden-properties: Some property names such as 'name' cause problems; jsure can detect static instances of those problematic names.
-list-props: Will list all the (static) property names used in the file.

Miscellaneous options

-quiet: Suppress informative messages
-no-warnings: Suppress warnings

Changing behaviour on certain subdirectories

Errors and warnings produced by source files whose name starts with a prefix given by an -ignorify (resp. -warnify) option will be ignored (resp. transformed into warnings).

Detection of anomalies

Anomalies, such as using an uninitialized variable, are legal language constructs that are bad coding practice or likely errors. Each anomaly has an associated action, which can be changed with a one-letter flag by an option. The actions are ignore (i), warn (w) or error (e).

Anomalies

-toplevel-bindings: Setting global properties without a "var".
-assigning-to-args: Assigning to a function argument.
-uninitialized-vars: Using uninitialized variables. In Javascript, uninitialized variables are set to undefined.

Unused identifiers

Jsure can detect unused variables (-unused-vars), arguments (-unused-args) or functions (-unused-funs). Sometimes it is unavoidable to have unused arguments - for example when you have to furnish a callback but have no need for all of its arguments. Jsure will ignore any variable, argument or function whose name starts with an underscore (_) will be ignored. (The rule for flagging unused variables can be changed with the -unused-ident-regexp option.) Using such a variable is an anomaly (-using-unused).

Summary of anomalies

-unused-args: Function arguments unused in the body of the function.
-using-unused: Using variables or arguments lexically declared to be unused
-unused-vars: Unused variables
-unused-funs: Unused functions
-shadowing-args: Arguments shadowed by variables
-dangling-commas: Dangling commas in object and array litterals

Not yet implemented:

-unreachable-code: Unreachable code

Environment variables

It is possible to change the behaviour of jsure thru the environment variables JSURE and JSURE_BEFORE. These variables define options to be processed before (JSURE_BEFORE) and after (JSURE) the processing of command-line options. The syntax for the environment variable is a little different than that of the command-line options. For instance, the set of command-line options

-toplevel-bindings: e -dont-catch

would translate to

  JSURE="toplevel_bindings=e;dont_catch"

In other words, the first dash (-) of the option names is to be removed, remaining dashes are to be replaced by underscores (_), options are to be separated by semicolons (;) and an equal sign (=) should separate option names from their arguments.

Excerpts and colorization

Jsure can show the context surrounding errors. This is settable with the -errors option: -errors t will display text, -errors p will only display the error position. The same thing applies to warnings with the -warnings option. Jsure can also brighten up your life by partially colorizing error or warning messages. These colors can be configured using the following options:

-info-color <color>: Info color
-warning-color <color>: Warning color
-error-color <color>: Error color
-number-color <color>: Line number color
-code-color <color>: Code color
-hl-color <color>: Code highlight color

Here, <color> is one of;

black
red
green
yellow
blue
magenta
cyan
white
none

and will produce corresponding ANSI escape sequences, which may or may not, given the configuration of your terminal, produce the expected colors.

Caching parse trees

To accelerate parsing, use the -cache <filename> option; jsure will then cache parse trees in the file <filename>.dir, which will also be linked to <filename>.pag (this behaviour is defined by your system's DBM library).