Match patterns

Match Patterns

The following patterns can be used as pattern arguments to check and Match.test:

Match.Any

Matches any value.

String, Number, Boolean, undefined, null

Matches a primitive of the given type.

Match.Integer

Matches a signed 32-bit integer. Doesn't match Infinity, -Infinity, or NaN.

[pattern]

A one-element array matches an array of elements, each of which match pattern. For example, [Number] matches a (possibly empty) array of numbers; [Match.Any] matches any array.

{key1: pattern1, key2: pattern2, ...}

Matches an Object with the given keys, with values matching the given patterns. If any pattern is a Match.Maybe or Match.Optional, that key does not need to exist in the object. The value may not contain any keys not listed in the pattern. The value must be a plain Object with no special prototype.

Match.ObjectIncluding({key1: pattern1, key2: pattern2, ...})

Matches an Object with the given keys; the value may also have other keys with arbitrary values.

Object

Matches any plain Object with any keys; equivalent to Match.ObjectIncluding({}).

Match.Maybe(pattern)

Matches either undefined, null, or pattern. If used in an object, matches only if the key is not set as opposed to the value being set to undefined or null. This set of conditions was chosen because undefined arguments to Meteor Methods are converted to null when sent over the wire.

// In an object
var pattern = { name: Match.Maybe(String) };
check({ name: "something" }, pattern) // OK
check({}, pattern) // OK
check({ name: undefined }, pattern) // Throws an exception
check({ name: null }, pattern) // Throws an exception

// Outside an object
check(null, Match.Maybe(String)); // OK
check(undefined, Match.Maybe(String)); // OK

Match.Optional(pattern)

Behaves like Match.Maybe except it doesn't accept null. If used in an object, the behavior is identical to Match.Maybe.

Match.OneOf(pattern1, pattern2, ...)

Matches any value that matches at least one of the provided patterns.

Any constructor function (eg, Date)

Matches any element that is an instance of that type.

Match.Where(condition)

Calls the function condition with the value as the argument. If condition returns true, this matches. If condition throws a Match.Error or returns false, this fails. If condition throws any other error, that error is thrown from the call to check or Match.test. Examples:

check(buffer, Match.Where(EJSON.isBinary));

NonEmptyString = Match.Where(function (x) {
  check(x, String);
  return x.length > 0;
});
check(arg, NonEmptyString);