feat: add boolean parser

README.md

@@ -28,6 +28,7 @@ to your definition of valid. See [how to use it](#usage).
   - [makeEnv(schema: Schema): Env](#makeenvschema-schema-env)
   - [Parsers](#parsers)
     - [parsers.string(value: string): string](#parsersstringvalue-string-string)
+    - [parsers.boolean(value: string): boolean](#parsersbooleanvalue-string-boolean)
     - [parsers.integer(value: string): number](#parsersintegervalue-string-number)
     - [parsers.float(value: string): float](#parsersfloatvalue-string-float)
     - [parsers.email(value: string): string](#parsersemailvalue-string-string)
@@ -137,6 +138,12 @@ Ensures required env variables are present and returns an env object.
 
 Trivial parser. It doesn't do any validation.
 
+#### parsers.boolean(value: string): boolean
+
+Ensures the value is a truthy or falsy value.
+Truthy values: 'true', '1', 'yes'.
+Falsy values: 'false', '0', 'no'.
+
 #### parsers.integer(value: string): number
 
 Ensures the value is an integer.

src/index.ts

@@ -1,4 +1,5 @@
 import {
+  boolean,
   email,
   float,
   integer,
@@ -16,6 +17,7 @@ import {
 
 const parsers = {
   string,
+  boolean,
   integer,
   float,
   email,

src/parsers.test.ts

@@ -10,6 +10,34 @@ describe('parsers.string', () => {
   });
 });
 
+describe('parsers.boolean', () => {
+  test('parses a truthy value', () => {
+    const serializedTruthyValues = ['true', '1', 'yes'];
+    const expectedValue = true;
+
+    serializedTruthyValues.forEach(serializedTruthyValue => {
+      expect(() => parsers.boolean(serializedTruthyValue)).not.toThrow();
+      expect(parsers.boolean(serializedTruthyValue)).toEqual(expectedValue);
+    });
+  });
+
+  test('parses a falsy value', () => {
+    const serializedFalsyValues = ['false', '0', 'no'];
+    const expectedValue = false;
+
+    serializedFalsyValues.forEach(serializedFalsyValue => {
+      expect(() => parsers.boolean(serializedFalsyValue)).not.toThrow();
+      expect(parsers.boolean(serializedFalsyValue)).toEqual(expectedValue);
+    });
+  });
+
+  test('throws when serialized value is not valid', () => {
+    const serializedValue = 'invalid';
+
+    expect(() => parsers.boolean(serializedValue)).toThrow();
+  });
+});
+
 describe('parsers.integer', () => {
   test('parses an integer', () => {
     const serializedValue = '10';

src/parsers.ts

@@ -7,6 +7,30 @@ export type Parser<TReturn = any> = (serializedValue: string) => TReturn;
  */
 export const string: Parser<string> = serializedValue => serializedValue;
 
+/**
+ * Parses a boolean. parsed values are case insensitive.
+ * Truthy values: true, 1, yes.
+ * Falsy values: false, 0, no.
+ */
+export const boolean: Parser<boolean> = serializedValue => {
+  const truthyValues = ['true', '1', 'yes'];
+  const falsyValues = ['false', '0', 'no'];
+
+  const lowercaseSerializedValue = serializedValue.toLowerCase();
+
+  if (truthyValues.includes(lowercaseSerializedValue)) {
+    return true;
+  }
+
+  if (falsyValues.includes(lowercaseSerializedValue)) {
+    return false;
+  }
+
+  const validValuesString = [...truthyValues, ...falsyValues].join(' ');
+
+  throw new Error(`value is not valid. Valid values: ${validValuesString}`);
+};
+
 /**
  * Parses an integer.
  */