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<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width">
  <title>bufferCount</title>
  <script src="https://npmcdn.com/@reactivex/rxjs@5.0.0-beta.3/dist/global/Rx.umd.js"></script>
</head>
<body>
</body>
</html>
 
const source = Rx.Observable.from([1,2,3,4,5]);
//no arguments, emit first value
const example = source.first();
//output: "First value: 1"
const subscribe = example.subscribe(val => console.log(`First value: ${val}`));
//emit first item to pass test
const exampleTwo = source.first(num => num === 5);
//output: "First to pass test: 5"
const subscribeTwo = exampleTwo.subscribe(val => console.log(`First to pass test: ${val}`));
//using optional projection function
const exampleThree = source.first(num => num % 2 === 0, 
                                    (result, index) => `First even: ${result} is at index: ${index}`);
//output: "First even: 2 at index: 1"
const subscribeThree = exampleThree.subscribe(val => console.log(val));
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