docs: add links to clarify truthy/falsy

lib/options/SchemaTypeOptions.js

@@ -107,7 +107,8 @@ Object.defineProperty(SchemaTypeOptions.prototype, 'ref', opts);
 Object.defineProperty(SchemaTypeOptions.prototype, 'select', opts);
 
 /**
- * If truthy, Mongoose will build an index on this path when the model is
+ * If [truthy](https://masteringjs.io/tutorials/fundamentals/truthy), Mongoose will
+ * build an index on this path when the model is
  * compiled.
  *
  * @api public
@@ -120,7 +121,8 @@ Object.defineProperty(SchemaTypeOptions.prototype, 'select', opts);
 Object.defineProperty(SchemaTypeOptions.prototype, 'index', opts);
 
 /**
- * If truthy, Mongoose will build a unique index on this path when the
+ * If [truthy](https://masteringjs.io/tutorials/fundamentals/truthy), Mongoose
+ * will build a unique index on this path when the
  * model is compiled. [The `unique` option is **not** a validator](/docs/validation.html#the-unique-option-is-not-a-validator).
  *
  * @api public
@@ -133,7 +135,8 @@ Object.defineProperty(SchemaTypeOptions.prototype, 'index', opts);
 Object.defineProperty(SchemaTypeOptions.prototype, 'unique', opts);
 
 /**
- * If truthy, Mongoose will disallow changes to this path once the document
+ * If [truthy](https://masteringjs.io/tutorials/fundamentals/truthy), Mongoose will
+ * disallow changes to this path once the document
  * is saved to the database for the first time. Read more about [immutability in Mongoose here](http://thecodebarbarian.com/whats-new-in-mongoose-5-6-immutable-properties.html).
  *
  * @api public
@@ -146,7 +149,8 @@ Object.defineProperty(SchemaTypeOptions.prototype, 'unique', opts);
 Object.defineProperty(SchemaTypeOptions.prototype, 'immutable', opts);
 
 /**
- * If truthy, Mongoose will build a sparse index on this path.
+ * If [truthy](https://masteringjs.io/tutorials/fundamentals/truthy), Mongoose will
+ * build a sparse index on this path.
  *
  * @api public
  * @property sparse
@@ -158,7 +162,8 @@ Object.defineProperty(SchemaTypeOptions.prototype, 'immutable', opts);
 Object.defineProperty(SchemaTypeOptions.prototype, 'sparse', opts);
 
 /**
- * If truthy, Mongoose will build a text index on this path.
+ * If [truthy](https://masteringjs.io/tutorials/fundamentals/truthy), Mongoose
+ * will build a text index on this path.
  *
  * @api public
  * @property text

lib/schema.js

@@ -1631,8 +1631,8 @@ Schema.prototype.indexes = function() {
  * @param {String|Model} [options.ref] model name or model instance. Marks this as a [populate virtual](populate.html#populate-virtuals).
  * @param {String|Function} [options.localField] Required for populate virtuals. See [populate virtual docs](populate.html#populate-virtuals) for more information.
  * @param {String|Function} [options.foreignField] Required for populate virtuals. See [populate virtual docs](populate.html#populate-virtuals) for more information.
- * @param {Boolean|Function} [options.justOne=false] Only works with populate virtuals. If truthy, will be a single doc or `null`. Otherwise, the populate virtual will be an array.
- * @param {Boolean} [options.count=false] Only works with populate virtuals. If truthy, this populate virtual will contain the number of documents rather than the documents themselves when you `populate()`.
+ * @param {Boolean|Function} [options.justOne=false] Only works with populate virtuals. If [truthy](https://masteringjs.io/tutorials/fundamentals/truthy), will be a single doc or `null`. Otherwise, the populate virtual will be an array.
+ * @param {Boolean} [options.count=false] Only works with populate virtuals. If [truthy](https://masteringjs.io/tutorials/fundamentals/truthy), this populate virtual will contain the number of documents rather than the documents themselves when you `populate()`.
  * @return {VirtualType}
  */
 

lib/schematype.js

@@ -664,7 +664,7 @@ SchemaType.prototype.get = function(fn) {
  *     Product.on('error', handleError);
  *
  * @param {RegExp|Function|Object} obj validator function, or hash describing options
- * @param {Function} [obj.validator] validator function. If the validator function returns `undefined` or a truthy value, validation succeeds. If it returns falsy (except `undefined`) or throws an error, validation fails.
+ * @param {Function} [obj.validator] validator function. If the validator function returns `undefined` or a truthy value, validation succeeds. If it returns [falsy](https://masteringjs.io/tutorials/fundamentals/falsy) (except `undefined`) or throws an error, validation fails.
  * @param {String|Function} [obj.message] optional error message. If function, should return the error message as a string
  * @param {Boolean} [obj.propsParameter=false] If true, Mongoose will pass the validator properties object (with the `validator` function, `message`, etc.) as the 2nd arg to the validator function. This is disabled by default because many validators [rely on positional args](https://github.com/chriso/validator.js#validators), so turning this on may cause unpredictable behavior in external validators.
  * @param {String|Function} [errorMsg] optional error message. If function, should return the error message as a string