range.js

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range.js

var AnythingStream = require('./anything');


var undef;

¶

RangeStream is a Readable stream that will produce a sequence of numbers starting from 'start', and ending at most at 'end'(no values greater than end can be emitted). The optional 'step' argument defaults to 1.
```
var RangeStream = AnythingStream.extend({
  constructor: function RangeStream(start, end, step) {
```
¶

Since we are emitting numbers, 'objectMode' is required
```
    AnythingStream.call(this, {objectMode: true});
```

If only the 'start' argument is provided, it will be considered as a range from 0 to 'start'

    if (end === undef || end === null) {
      end = start;
      start = 0;
    }

    this._current = start;
    this._end = end;
    this._step = step || 1;
  },

  _next: function() {
    var rv = this._current;

¶

The '_update' method is implemented by a subclass, and will either increment or decrement the value depending on the comparison of the 'start' and 'end' parameters
```
    this._update();
    return rv;
  }
});


var IncreasingRangeStream = RangeStream.extend({
```

The constructor is only defined to improve debugging experience

  constructor: function IncreasingRangeStream(start, end, step) {
    RangeStream.call(this, start, end, step);
  },

  _done: function() { return this._current > this._end; },

  _update: function() { this._current += this._step; }
});


var DecreasingRangeStream = RangeStream.extend({
  constructor: function DecreasingRangeStream(start, end, step) {
    RangeStream.call(this, start, end, step);
  },

  _done: function() { return this._current < this._end; },

  _update: function() { this._current -= this._step; }
});


module.exports = function range(start, end, step) {
  return end === undef || end === null || start < end ?
    new IncreasingRangeStream(start, end, step) : 
    new DecreasingRangeStream(start, end, step);
};