Preconditions for Node.js

Precondition checks for Node.js.

Installation

npm install precond

Unit tests

npm test

Usage

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 will both produce the same stack trace.

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

API

Checks

Provided checks are the following:

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

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

• expression: an expression to test for trueness
• messageFormat: error message format template
• formatArgs: arguments to be substituted into the message template

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

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

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

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

Ensure that expression is defined (could be null). Throws an IllegalArgumentError if expression is undefined.

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

Ensure that expression is defined and not null. Throws an IllegalArgumentError if expression is undefined or null.

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

Ensure that expression is an array. Throws an IllegalArgumentError if expression isn't an array.

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

Ensure that expression is a number. Throws an IllegalArgumentError if expression isn't a number.

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

Ensure that expression is a boolean. Throws an IllegalArgumentError if expression isn't a boolean.

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

Ensure that expression is a function. Throws an IllegalArgumentError if expression isn't a function.

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

Ensure that expression is an object. Throws an IllegalArgumentError if expression isn't an object.

Errors

precond.IllegalArgumentError

Extends Error and is thrown to signal illegal arguments.

precond.IllegalStateError

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

License

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