first

Returns the first element of an observable sequence that satisfies the condition in the predicate, or a default value if no such element exists. If no default value is given, then onError will be called.

Arguments

Rx.Observable.prototype.first([predicate], [thisArg], [defaultValue])

1. [predicate] (Function): A predicate function to evaluate for elements in the source sequence. The callback is called with the following information:

   1. the value of the element

   2. the index of the element

   3. the Observable object being subscribed

2. [thisArg] (Any): Object to use as this when executing the predicate.

3. [defaultValue] (Any): Default value if no such element exists.

Rx.Observable.prototype.first([settings])

1. [settings] (Object): An object with the following fields

   • [predicate] (Function): A predicate function to evaluate for elements in the source sequence. The callback is called with the following information:

     1. the value of the element

     2. the index of the element

     3. the Observable object being subscribed

   • [thisArg] (Any): Object to use as this when executing the predicate.

   • [defaultValue] (Any): Default value if no such element exists.

Returns

(Observable): An observable sequence that contains elements from the input sequence that satisfy the condition.

Example

No Match

Without a predicate

With a predicate

/* With a default value */
var source = Rx.Observable.range(0, 10)
  .first({
    predicate: function (x, idx, obs) { return x > 10; },
    defaultValue: 42
  });


var subscription = source.subscribe(
  function (x) {
    console.log('Next: %s', x);
  },
  function (err) {
    console.log('Error: %s', err);
  },
  function () {
    console.log('Completed');
  });

// => Next: 42
// => Completed