property set equal to the value of the `message` parameter. If the `message`

parameter is undefined, a default error message is assigned.

## assert.fail(actual, expected, message, operator)

## assert.fail(actual, expected[, message[, operator[, stackStartFunction]]])

<!-- YAML

added: v0.1.21

-->

* `actual` {any}

* `expected` {any}

* `message` {any}

* `operator` {string}

* `stackStartFunction` {function} (default: `assert.fail`)

Throws an `AssertionError`. If `message` is falsy, the error message is set as

the values of `actual` and `expected` separated by the provided `operator`.

Otherwise, the error message is the value of `message`.

If `stackStartFunction` is provided, all stack frames above that function will

be removed from stacktrace (see [`Error.captureStackTrace`]).

```js

const assert = require('assert');

assert.fail(1, 2, undefined, '>');

// AssertionError: 1 > 2

assert.fail(1, 2, 'fail');

// AssertionError: fail

assert.fail(1, 2, 'whoops', '>');

// AssertionError: whoops

```

Example use of `stackStartFunction` for truncating the exception's stacktrace:

```js

function suppressFrame() {

assert.fail('a', 'b', undefined, '!==', suppressFrame);

}

suppressFrame();

// AssertionError: 'a' !== 'b'

// at repl:1:1

// at ContextifyScript.Script.runInThisContext (vm.js:44:33)

// ...

```

## assert.ifError(value)

<!-- YAML

added: v0.1.97

[`assert.ok()`]: #assert_assert_ok_value_message

[`assert.throws()`]: #assert_assert_throws_block_error_message

[`Error`]: errors.html#errors_class_error

[`Error.captureStackTrace`]: errors.html#errors_error_capturestacktrace_targetobject_constructoropt

[`RegExp`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions

[`TypeError`]: errors.html#errors_class_typeerror