Add module for merging multiple streams.

Author: Jordalgo

module/mergeall/README.md

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+# flyd-mergeall
+Flyd module for merging several streams into one.
+
+__Signature__
+
+`[Stream a] -> Stream a`
+
+__Example__
+
+```javascript
+var s1 = flyd.stream();
+var s2 = flyd.stream();
+var s3 = flyd.stream();
+var merged = mergeAll([s1, s2, s3]);
+s1(1);
+s2(2);
+console.log(merged()); // logs 2
+```
+

module/mergeall/index.js

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+var flyd = require('../../lib');
+
+module.exports = function mergeAll(streams) {
+  var s = flyd.immediate(flyd.combine(function() {
+    var self = arguments[arguments.length - 2];
+    if (arguments[arguments.length - 1][0]) {
+      self(arguments[arguments.length - 1][0]());
+      return;
+    }
+    [].slice.call(arguments, 0, arguments.length - 2)
+    .some(function(s1) {
+      if (s1.hasVal) {
+        self(s1.val);
+        return true;
+      }
+    });
+  }, streams));
+  flyd.endsOn(flyd.combine(function() {
+    return true;
+  }, streams.map(function(sm) { return sm.end; })), s);
+  return s;
+};
+

module/mergeall/test/index.js

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+var assert = require('assert');
+var flyd = require('../../../lib');
+var stream = flyd.stream;
+
+var mergeAll = require('../index.js');
+
+describe('mergeAll', function() {
+  it('merges multiple streams', function() {
+    var s1 = stream();
+    var s2 = stream();
+    var s3 = stream();
+    var merged = mergeAll([s1, s2, s3]);
+    s1(1);
+    assert.equal(merged(), 1);
+    s2(2);
+    assert.equal(merged(), 2);
+    s3(3);
+    assert.equal(merged(), 3);
+    s2('hello');
+    assert.equal(merged(), 'hello');
+  });
+  it('has initial value', function() {
+    var s1 = stream(1);
+    var s2 = stream(2);
+    var s3 = stream();
+    var merged = mergeAll([s1, s2, s3]);
+    assert.equal(merged(), 1);
+    s3(3);
+    assert.equal(merged(), 3);
+  });
+  it('ends when all the merged streams end', function() {
+    var s1 = stream();
+    var s2 = stream();
+    var s3 = stream();
+    var merged = mergeAll([s1, s2, s3]);
+    s1.end(true);
+    assert.equal(s1.end(), true);
+    assert.equal(merged.end(), undefined);
+    s2.end(true);
+    assert.equal(s2.end(), true);
+    assert.equal(merged.end(), undefined);
+    s3.end(true);
+    assert.equal(s3.end(), true);
+    assert.equal(merged.end(), true);
+  });
+});