How to use the core-util-is.isError function in core-util-is

set (value) {
      if (isError(value)) {
        return value
      }

      return new Error(value)
    }
  }

function parseConstructorArguments(args)
{
	var argv, options, sprintf_args, shortmessage, k;

	mod_assertplus.object(args, 'args');
	mod_assertplus.bool(args.strict, 'args.strict');
	mod_assertplus.array(args.argv, 'args.argv');
	argv = args.argv;

	/*
	 * First, figure out which form of invocation we've been given.
	 */
	if (argv.length === 0) {
		options = {};
		sprintf_args = [];
	} else if (mod_isError(argv[0])) {
		options = { 'cause': argv[0] };
		sprintf_args = argv.slice(1);
	} else if (typeof (argv[0]) === 'object') {
		options = {};
		for (k in argv[0]) {
			options[k] = argv[0][k];
		}
		sprintf_args = argv.slice(1);
	} else {
		mod_assertplus.string(argv[0],
		    'first argument to VError, SError, or WError ' +
		    'constructor must be a string, object, or Error');
		options = {};
		sprintf_args = argv;
	}

function parseConstructorArguments(args)
{
	var argv, options, sprintf_args, shortmessage, k;

	mod_assertplus.object(args, 'args');
	mod_assertplus.bool(args.strict, 'args.strict');
	mod_assertplus.array(args.argv, 'args.argv');
	argv = args.argv;

	/*
	 * First, figure out which form of invocation we've been given.
	 */
	if (argv.length === 0) {
		options = {};
		sprintf_args = [];
	} else if (mod_isError(argv[0])) {
		options = { 'cause': argv[0] };
		sprintf_args = argv.slice(1);
	} else if (typeof (argv[0]) === 'object') {
		options = {};
		for (k in argv[0]) {
			options[k] = argv[0][k];
		}
		sprintf_args = argv.slice(1);
	} else {
		mod_assertplus.string(argv[0],
		    'first argument to VError, SError, or WError ' +
		    'constructor must be a string, object, or Error');
		options = {};
		sprintf_args = argv;
	}

VError.findCauseByName = function (err, name)
{
	var cause;

	mod_assertplus.ok(mod_isError(err), 'err must be an Error');
	mod_assertplus.string(name, 'name');
	mod_assertplus.ok(name.length > 0, 'name cannot be empty');

	for (cause = err; cause !== null; cause = VError.cause(cause)) {
		mod_assertplus.ok(mod_isError(cause));
		if (cause.name == name) {
			return (cause);
		}
	}

	return (null);
};

errors.forEach(function (e) {
		mod_assertplus.ok(mod_isError(e));
	});

VError.findCauseByName = function (err, name)
{
	var cause;

	mod_assertplus.ok(mod_isError(err), 'err must be an Error');
	mod_assertplus.string(name, 'name');
	mod_assertplus.ok(name.length > 0, 'name cannot be empty');

	for (cause = err; cause !== null; cause = VError.cause(cause)) {
		mod_assertplus.ok(mod_isError(cause));
		if (cause.name == name) {
			return (cause);
		}
	}

	return (null);
};

WError.prototype.cause = function we_cause(c)
{
	if (mod_isError(c))
		this.jse_cause = c;

	return (this.jse_cause);
};

VError.findCauseByName = function (err, name)
{
	var cause;

	mod_assertplus.ok(mod_isError(err), 'err must be an Error');
	mod_assertplus.string(name, 'name');
	mod_assertplus.ok(name.length > 0, 'name cannot be empty');

	for (cause = err; cause !== null; cause = VError.cause(cause)) {
		mod_assertplus.ok(mod_isError(cause));
		if (cause.name == name) {
			return (cause);
		}
	}

	return (null);
};

errors.forEach(function (e) {
		mod_assertplus.ok(mod_isError(e));
	});

WError.prototype.cause = function we_cause(c)
{
	if (mod_isError(c))
		this.jse_cause = c;

	return (this.jse_cause);
};