js-format/README.md

@e22m4u/js-format

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Extended version of the format utility for Node.js

• standard specifiers %s, %d, and %j
• added %v for outputting primitive values and constructor names
• added %l for outputting a comma-separated list "foo", 10, true

Additionally:

• built-in Errorf class with error message interpolation

Installation

npm install @e22m4u/js-format

To load the ES-module, you need to set "type": "module" in the package.json file, or use the .mjs extension.

Examples

ES-import

import {format} from '@e22m4u/js-format';

%v

Strings are wrapped in quotes, other primitives are converted to strings, and for more complex types the constructor name is output.

format('It is %v', 'foo');        // It is "foo"
format('It is %v', '');           // It is ""
format('It is %v', 10);           // It is 10
format('It is %v', 0);            // It is 0
format('It is %v', NaN);          // It is NaN
format('It is %v', Infinity);     // It is Infinity
format('It is %v', true);         // It is true
format('It is %v', false);        // It is false
format('It is %v', {foo: 'bar'}); // It is Object
format('It is %v', new Date());   // It is Date
format('It is %v', new Map());    // It is Map
format('It is %v', () => 10);     // It is Function
format('It is %v', undefined);    // It is undefined
format('It is %v', null);         // It is null

The %v specifier was designed to output values in error messages when it's important to have an idea of their types. However, outputting the contents of an object may be excessive for such a task. For this reason, objects are converted to the constructor name, which allows for a relatively accurate determination of the output value's type.

class MyClass {}

format('It is %v', 'MyClass');     // It is "MyClass"
format('It is %v', MyClass);       // It is MyClass
format('It is %v', new MyClass()); // It is MyClass (instance)

%l

Outputs array elements separated by commas.

format('An array of %l', ['foo', 10, true]);
// An array of "foo", 10, true

Array elements are converted to strings following the logic of the %v specifier.

The Errorf class

The Errorf class constructor passes arguments to the format function to form an error message.

Example:

import {Errorf} from '@e22m4u/js-format';

throw new Errorf(
  'It requires one of %l, but %v given.',
  [true, false, 'y', 'n'],
  new Map(),
);
// Error: It requires one of true, false, "y", "n", but Map given.

Tests

npm run test

License

MIT