nodejs/lib/console.js

'use strict';

const util = require('util');

function Console(stdout, stderr, ignoreErrors = true) {
  if (!(this instanceof Console)) {
    return new Console(stdout, stderr, ignoreErrors);
  }
  if (!stdout || typeof stdout.write !== 'function') {
    throw new TypeError('Console expects a writable stream instance');
  }
  if (!stderr) {
    stderr = stdout;
  } else if (typeof stderr.write !== 'function') {
    throw new TypeError('Console expects writable stream instances');
  }

  var prop = {
    writable: true,
    enumerable: false,
    configurable: true
  };
  prop.value = stdout;
  Object.defineProperty(this, '_stdout', prop);
  prop.value = stderr;
  Object.defineProperty(this, '_stderr', prop);
  prop.value = ignoreErrors;
  Object.defineProperty(this, '_ignoreErrors', prop);
  prop.value = new Map();
  Object.defineProperty(this, '_times', prop);
  prop.value = createWriteErrorHandler(stdout);
  Object.defineProperty(this, '_stdoutErrorHandler', prop);
  prop.value = createWriteErrorHandler(stderr);
  Object.defineProperty(this, '_stderrErrorHandler', prop);

  // bind the prototype functions to this Console instance
  var keys = Object.keys(Console.prototype);
  for (var v = 0; v < keys.length; v++) {
    var k = keys[v];
    this[k] = this[k].bind(this);
  }
}

// Make a function that can serve as the callback passed to `stream.write()`.
function createWriteErrorHandler(stream) {
  return (err) => {
    // This conditional evaluates to true if and only if there was an error
    // that was not already emitted (which happens when the _write callback
    // is invoked asynchronously).
    if (err && !stream._writableState.errorEmitted) {
      // If there was an error, it will be emitted on `stream` as
      // an `error` event. Adding a `once` listener will keep that error
      // from becoming an uncaught exception, but since the handler is
      // removed after the event, non-console.* writes won’t be affected.
      stream.once('error', noop);
    }
  };
}

function write(ignoreErrors, stream, string, errorhandler) {
  if (!ignoreErrors) return stream.write(string);

  // There may be an error occurring synchronously (e.g. for files or TTYs
  // on POSIX systems) or asynchronously (e.g. pipes on POSIX systems), so
  // handle both situations.
  try {
    // Add and later remove a noop error handler to catch synchronous errors.
    stream.once('error', noop);

    stream.write(string, errorhandler);
  } catch (e) {
    // Sorry, there’s no proper way to pass along the error here.
  } finally {
    stream.removeListener('error', noop);
  }
}


// As of v8 5.0.71.32, the combination of rest param, template string
// and .apply(null, args) benchmarks consistently faster than using
// the spread operator when calling util.format.
Console.prototype.log = function log(...args) {
  write(this._ignoreErrors,
        this._stdout,
        `${util.format.apply(null, args)}\n`,
        this._stdoutErrorHandler);
};


Console.prototype.info = Console.prototype.log;


Console.prototype.warn = function warn(...args) {
  write(this._ignoreErrors,
        this._stderr,
        `${util.format.apply(null, args)}\n`,
        this._stderrErrorHandler);
};


Console.prototype.error = Console.prototype.warn;


Console.prototype.dir = function dir(object, options) {
  options = Object.assign({customInspect: false}, options);
  write(this._ignoreErrors,
        this._stdout,
        `${util.inspect(object, options)}\n`,
        this._stdoutErrorHandler);
};


Console.prototype.time = function time(label) {
  this._times.set(label, process.hrtime());
};


Console.prototype.timeEnd = function timeEnd(label) {
  const time = this._times.get(label);
  if (!time) {
    process.emitWarning(`No such label '${label}' for console.timeEnd()`);
    return;
  }
  const duration = process.hrtime(time);
  const ms = duration[0] * 1000 + duration[1] / 1e6;
  this.log('%s: %sms', label, ms.toFixed(3));
  this._times.delete(label);
};


Console.prototype.trace = function trace(...args) {
  // TODO probably can to do this better with V8's debug object once that is
  // exposed.
  var err = new Error();
  err.name = 'Trace';
  err.message = util.format.apply(null, args);
  Error.captureStackTrace(err, trace);
  this.error(err.stack);
};


Console.prototype.assert = function assert(expression, ...args) {
  if (!expression) {
    require('assert').ok(false, util.format.apply(null, args));
  }
};


module.exports = new Console(process.stdout, process.stderr);
module.exports.Console = Console;

function noop() {}