Arg Utils

Utility library for argument validations. Provides modules for function argument validations and JSON schema validations. Function argument checks are important in loosely typed languages such as javascript, and a good development practice is to explicitly check each function argument prior to using it, like this:

function sayHello(name, lang) {
    if(typeof name !== 'string' || name.length <= 0) {
        throw new Error('Invalid name argument (arg #1)');
    }
    if(typeof lang !== 'string' || lang.length <= 0) {
        lang = 'english';
    }
}

In other situations (ex: AWS Lambda functions), the function may accept a simple object as an input, but expect that the object conforms to a specific schema.

This library makes it syntactically nicer to perform such checks, by providing utility methods for both argument checks and schema validation.

API Documentation

API documentation can be found here.

Installation

This library can be installed via npm using:

npm install @vamship/arg-utils

Usage

This libary exports two modules:

• schemaHelper: Generates a schema validator function based on a schema object. This function can then be used to validate inputs against this schema.
• argValidator: Provides basic argument validation functionality for function input validation.

Release Notes

V2.0.0

This version introduces breaking changes in order to find a better balance between "syntactic niceness" and performance. V1.x allowed error checks and default settings to be applied by allowing chained function calls, for example:

    _argValidator.checkString(someArg).throw('some error');

While one could argue that this made the code more readable, quick performance tests showed that these checks were multiple orders of magnitude slower than simple error checks using if-then-else statements. The fact that they are slower was expected, but how much slower they really were was a surprise.

Version 2.0.0 changes the validator signatures to accept the error message as a part of the check function, and throws immediately, like this:

    _argValidator.checkString(someArg, 1, 'some error'); // Throws an error.

    _argValidator.checkString(someArg, 1); // Does not throw, returns false.

Examples

Argument Validation

const _argValidator = require('@vamship/arg-validator').argValidator;

...

function sayHello(name, lang) {
    _argValidator.checkString(name, 1, 'Invalid name (arg #1)');
    if(!_argValidator.checkString(lang, 1)){
        lang = 'english';
    }
}

Schema Validation

const _schemaHelper = require('@vamship/arg-validator').schemaHelper;
const schema = require('<path to json schema>');
const checkSchema = _schemaHelper.createSchemaChecker(schema);

...

function processInput(input) {
    checkSchema(input, true) // Throws a schema error
}

...

function processInput(input) {
    if(!checkSchema(input)) { // Does not throw an error, but returns false

        // Perform some actions on schema validation failure
    }
}