JS: Logging and String Formatting

Logging and String Formatting¶

Source code: src/helpers.js, src/sprintf.js

Every writer takes a format and its arguments, in the style of printf. There is no gobj parameter and no error code, which the C API has. The JS runtime is simpler.

Write a log¶

log_error(format, ...args)¶

Writes an error. It goes to the remote handler too.

log_warning(format, ...args)¶

Writes a warning. It goes to the remote handler too.

log_info(format, ...args)¶

Writes an information message. It stays in the console.

log_debug(format, ...args)¶

Writes a debug message. It stays in the console.

Write a trace¶

trace_msg(format, ...args)¶

Writes one line of trace.

trace_json(json, msg)¶

Writes a JSON value.

Turn the levels on and off with the functions in Traces.

Where the logs go¶

set_remote_log_functions(remote_log_fn)¶

Sends the errors and the warnings to one handler, such as a websocket that carries them to a log centre. The information and the debug messages stay in the console.

set_log_callback(callback)¶

Sends every log to one function of the application.

set_console_log_enabled(enabled)¶

Turns the write to the console on or off.

set_console_log_filter(fn)¶

Gives one function the say over each console line, on top of the switch above. fn(level, msg) gives true to write the line. null writes them all, which is the default.

The console write occurs before the log callback runs, so nothing after it can remove a line. This is the only place to keep a class of lines off the console — for example, the timer traffic of the machine trace.

The filter decides the console only. The callback still gets every line. A filter that throws is ignored: a broken filter must not silence the log.

Format a string¶

sprintf(format, ...args)¶

Builds a string in the style of printf.

vsprintf(fmt, argv)¶

The same, and it takes the arguments in an array.

The conversions¶