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

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

into a more compact and declarative check bellow.

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(expression, [messageFormat, [formatArgs, ...]])
• checkState(expression, [messageFormat, [formatArgs, ...]])
• checkIsDef(expression, [messageFormat, [formatArgs, ...]]) -> expression
• checkIsDefAndNotNull(expression, [messageFormat, [formatArgs, ...]]) -> expression
• checkIsArray(expression, [messageFormat, [formatArgs, ...]]) -> expression
• checkIsNumber(expression, [messageFormat, [formatArgs, ...]]) -> expression
• checkIsBoolean(expression, [messageFormat, [formatArgs, ...]]) -> expression
• checkIsFunction(expression, [messageFormat, [formatArgs, ...]]) -> expression
• checkIsObject(expression, [messageFormat, [formatArgs, ...]]) -> expression

API

Static functions

precond.checkArgument(expression, [messageFormat, [formatArgs, ...]])

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

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

precond.checkState(expression, [messageFormat, [formatArgs, ...]])

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

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

precond.checkIsDef(expression, [messageFormat, [formatArgs, ...]])

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

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

precond.checkIsDefAndNotNull(expression, [messageFormat, [formatArgs, ...]])

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

precond.checkIsArray(expression, [messageFormat, [formatArgs, ...]])

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

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

precond.checkIsNumber(expression, [messageFormat, [formatArgs, ...]])

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

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

precond.checkIsBoolean(expression, [messageFormat, [formatArgs, ...]])

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

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

precond.checkIsFunction(expression, [messageFormat, [formatArgs, ...]])

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

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

precond.checkIsObject(expression, [messageFormat, [formatArgs, ...]])

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

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

Class precond.IllegalArgumentError

Extends Error and is thrown to signal illegal arguments.

Class precond.IllegalStateError

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.