Starters ​

Starter is used to create an iterable. A query must start with a starter operator. This page introduces the builtin functions that create starters.

NOTE: You can also define custom starters see Extensibility for more details.

Empty ​

Creates a Starter that returns an empty Iterable. Can be useful if you need an empty Iterable with zero memory allocation.

function empty<T>(): Starter<T>

function empty<T>(): Starter<T>

Example ​

const result = query(empty<number>())

for (const item of result) {
  console.log(item)
}

const result = query(empty<number>())

for (const item of result) {
  console.log(item)
}

Output ​

From ​

Creates a Starter that returns the Iterable it receives as an argument. This is the most common query starter, and the main way of transforming the builtin collections into query sources.

function from<T>(source: Iterable<T>): Starter<T>

function from<T>(source: Iterable<T>): Starter<T>

Arguments ​

• source: Iterable<T> - Contains the items to return

Example ​

const result = query(from([1, 2, 3]))

for (const item of result) {
  console.log(item)
}

const result = query(from([1, 2, 3]))

for (const item of result) {
  console.log(item)
}

Output ​

1
2
3

1
2
3

Range ​

Creates a Starter that generates an Iterable that contains a range of sequential numbers. It uses a generator to achieve this, so the actual numbers are not materialized in a collection.

NOTE: This operator uses deferred execution. The actual operation will be evaluated each time when the query result is iterated over.

function range(start: number, count: number): Starter<number>

function range(start: number, count: number): Starter<number>

Arguments ​

• start: number - The starting value of the generated Iterable
• count: number - The length of the generated Iterable

Example ​

const result = query(range(10, 3))

for (const item of result) {
  console.log(item)
}

const result = query(range(10, 3))

for (const item of result) {
  console.log(item)
}

Output ​

10
11
12

10
11
12

Repeat ​

Creates a Starter that generates an Iterable that contains a provided item multiple times. It uses a generator to achieve this, so the actual items are not materialized in a collection.

NOTE: This operator uses deferred execution. The actual operation will be evaluated each time when the query result is iterated over.

function repeat<T>(item: T, times: number): Starter<T>

function repeat<T>(item: T, times: number): Starter<T>

Arguments ​

• item: T - The item to repeat
• times: number - The amount of times to repeat the item

Example ​

const result = query(repeat('hello', 3))

for (const item of result) {
  console.log(item)
}

const result = query(repeat('hello', 3))

for (const item of result) {
  console.log(item)
}

Output ​

hello
hello
hello

hello
hello
hello