Add length.

doc/API.md

@@ -18,6 +18,7 @@
     - [filter(callbackfn[, thisArg]) -> Channel](#filtercallbackfn-thisarg---channel)
     - [forEach(callbackfn[, thisArg]) -> async](#foreachcallbackfn-thisarg---async)
     - [join(separator) -> async String](#joinseparator---async-string)
+    - [length](#length)
     - [map(callbackfn[, thisArg]) -> Channel](#mapcallbackfn-thisarg---channel)
     - [push(value) -> async bufferLength](#pushvalue---async-bufferlength)
     - [reduce(callbackfn[, initialValue])](#reducecallbackfn-initialvalue)
@@ -232,6 +233,10 @@ The values of the channel are converted to Strings, and these Strings are then
 concatenated, separated by occurrences of the separator. If no separator is
 provided, a single comma is used as the separator.
 
+### length
+
+The length of the channel's buffer.
+
 ### map(callbackfn[, thisArg]) -> Channel
 
 `callbackfn` should be a function that accepts one argument. `map` calls

lib/index.js

@@ -254,7 +254,11 @@ const Channel = function(bufferLength = 0) {
     }
   });
 
-  Object.defineProperty(readOnly, `value`, { get: () => lastValue });
+  Object.defineProperties(readOnly, {
+    length: { get: () => bufferLength },
+    value: { get: () => lastValue }
+  });
+
   Object.freeze(readOnly);
 
   const writeOnly = Object.freeze({

test/index.js

@@ -217,6 +217,10 @@ describe(`Channel object`, function() {
     assert.equal(await Channel.of(`a`, `b`, `c`).join(), `a,b,c`);
   });
 
+  it(`length`, function() {
+    assert.equal(Channel(42).length, 42);
+  });
+
   it(`map`, async function() {
     assert.deepEqual(
       await Channel.of(`a`, `b`, `c`)