Preconditions for Node.js


Precondition checks for Node.js inspired by Guava's precondition checking
utilities.

Installation

``
npm install precond
`

Unit tests

`
npm test
`

Overview

Precond provides a set of functions to verify arguments and state correctness

It lets you rewrite constructs like the following

`js
if (!this.isConnected) {
throw new Error('Client should be connected before calling X.');
}
`

into a more compact and declarative check bellow.

`js
precond.checkState(this.isConnected, 'Client should be ...');
`

**Note that even though the throw statement is wrapped in a function, the call
stack will still start from the calling function. So the previous examples would
both produce the same stack trace.**

All arguments after the message will be used to format the actual error
message that will be thrown.

The following precondition checks are provded:

- checkArgument(value, [messageFormat, [formatArgs, ...]])
- checkState(value, [messageFormat, [formatArgs, ...]])
- checkIsDef(value, [messageFormat, [formatArgs, ...]]) -> value
- checkIsDefAndNotNull(value, [messageFormat, [formatArgs, ...]]) -> value
- checkIsString(value, [messageFormat, [formatArgs, ...]]) -> value
- checkIsArray(value, [messageFormat, [formatArgs, ...]]) -> value
- checkIsNumber(value, [messageFormat, [formatArgs, ...]]) -> value
- checkIsBoolean(value, [messageFormat, [formatArgs, ...]]) -> value
- checkIsFunction(value, [messageFormat, [formatArgs, ...]]) -> value
- checkIsObject(value, [messageFormat, [formatArgs, ...]]) -> value

API

$3

#### precond.checkArgument(value, [messageFormat, [formatArgs, ...]])

- value: the value that is required to be truthy
- messageFormat: error message format template
- formatArgs: arguments to be substituted into the message template

Ensures that value is true. Throws an IllegalArgumentError if value
is false.

#### precond.checkState(value, [messageFormat, [formatArgs, ...]])

- value: the value that is required to be truthy
- messageFormat: error message format template
- formatArgs: arguments to be substituted into the message template

Ensures that value is true. Throws an IllegalStateError if value
is false.

#### precond.checkIsDef(value, [messageFormat, [formatArgs, ...]])

- value: the value that is required to be defined
- messageFormat: error message format template
- formatArgs: arguments to be substituted into the message template

Ensures that value is defined (could be null). Throws an
IllegalArgumentError if value is undefined. Returns the value of
the value that was validated.

#### precond.checkIsDefAndNotNull(value, [messageFormat, [formatArgs, ...]])

- value: the value that is required to be defined and not null
- messageFormat: error message format template
- formatArgs: arguments to be substituted into the message template

Ensures that value is defined and not null. Throws an
IllegalArgumentError if value is undefined or null. Returns the value of
the value that was validated.

#### precond.checkIsString(value, [messageFormat, [formatArgs, ...]])

- value: the value that is required to be a string
- messageFormat: error message format template
- formatArgs: arguments to be substituted into the message template

Ensures that value is a string or a String object. Throws an
IllegalArgumentError if value isn't a string. Returns the value of
the value that was validated.

#### precond.checkIsArray(value, [messageFormat, [formatArgs, ...]])

- value: the value that is required to be an array
- messageFormat: error message format template
- formatArgs: arguments to be substituted into the message template

Ensures that value is an array. Throws an IllegalArgumentError if
value isn't an array. Returns the value of the value that was
validated.

#### precond.checkIsNumber(value, [messageFormat, [formatArgs, ...]])

- value: the value that is required to be a number
- messageFormat: error message format template
- formatArgs: arguments to be substituted into the message template

Ensures that value is a number. Throws an IllegalArgumentError if
value isn't a number. Returns the value of the value that was
validated.

#### precond.checkIsBoolean(value, [messageFormat, [formatArgs, ...]])

- value: the value that is required to be a boolean
- messageFormat: error message format template
- formatArgs: arguments to be substituted into the message template

Ensures that value is a boolean. Throws an IllegalArgumentError if
value isn't a boolean. Returns the value of the value that was
validated.

#### precond.checkIsFunction(value, [messageFormat, [formatArgs, ...]])

- value: the value that is required to be a function
- messageFormat: error message format template
- formatArgs: arguments to be substituted into the message template

Ensures that value is a function. Throws an IllegalArgumentError if
value isn't a function. Returns the value of the value that was
validated.

#### precond.checkIsObject(value, [messageFormat, [formatArgs, ...]])

- value: the value that is required to be an object
- messageFormat: error message format template
- formatArgs: arguments to be substituted into the message template

Ensures that value is an object. Throws an IllegalArgumentError if
value isn't an object. Returns the value of the value that was
validated.

$3

Extends Error and is thrown to signal illegal arguments.

$3

Extends Error` and is thrown to signal that the program or object has reached
an illegal state.

License

This code is free to use under the terms of the MIT license.