api.md

append([val1[,val2[,...[,valN]]]]) ⇒ Seq

Creates a new sequence that appends the passed value to the existing seq. This method does not change the existing sequence.

Returns: Seq - A new sequence.
Throws:

• TypeError if the existing sequence is null or undefined when invoke via call/apply/bind.

Param	Description
...others	Iterable, iterator, generator function, array-like object, or single value to concatenate into new sequence. If omitted, the method returns the existing sequence.

Example

const seq = Seq.of(1, 2, 3);
const result = seq.append([4, 5, 6], { seven: 7 }, [[8], [9]], [[[10], [11]]]);
console.log(result.toArray());
// => [ 1, 2, 3, 4, 5, 6, { seven: 7 }, [ 8 ], [ 9 ], [ [ 10 ], [ 11 ] ] ]

• countBy(projection) ⇒ Seq

Applies a key-generating function to each element of a sequence and returns a sequence yielding unique keys and their number of occurrences in the original sequence. This method should not be used with large or infinite sequences.

Returns: Seq - The result sequence.
Throws:

• TypeError If the source sequence is null or undefined when invoke via call/apply/bind; or projection is a generator function or not a function.

Param	Description
projection	A function transforming each item of the input sequence into a key to be compared against the others.

Example

class Person {
  constructor(name) {
    this.Name = name;
  }
}
const mrA = new Person('A', 20);
const mrB = new Person('B', 15);
const seq = Seq.of(mrA, mrA, mrB);
const nameCounts = seq.countBy(x => x.Name).toArray();
console.log(nameCounts)
// => [['A', 2], ['B', 1]]

Seq.empty() ⇒ Seq

Creates an empty sequence.

Returns: Seq - An empty sequence.
Example

const emptySeq = Seq.empty();
console.log(emptySeq.toArray());
// => []

exists(predicate) ⇒ Seq

Tests if at least one element in the sequence passes the test implemented by the provided function.

Returns: boolean - true if the callback function returns a truthy value for at least one element in the sequence. Otherwise, false.
Throws:

• If the source sequence is null or undefined when invoke via call/apply/bind; or predicate is a generator function or not a function.

Param	Type	Description
predicate	function	A function to test on the elements of the seq.

Example

const seq = Seq.of(1,2,3,4,5);
const result = seq.exists(x => x % 2 === 0);
console.log(result);
// => true

filter(predicate) ⇒ Seq

Returns a new sequence containing only the elements of the collection for which the given predicate returns "true".

Returns: Seq - The result sequence.
Throws:

• TypeError If the source sequence is null or undefined when invoke via call/apply/bind; or predicate is a generator function or not a function.

Param	Type	Description
predicate	function	A function to test whether each item in the input sequence should be included in the output.

Example

const seq = Seq.of(1,2,3,4,5).filter(x => x % 2 === 0);
console.log([...seq]);
// => [2, 4]

findBack(predicate) ⇒ Seq

Returns the last element of a sequence that satisfies a specified condition.

Returns: The last element in the sequence that passes the test in the specified predicate function.
Throws:

• TypeError If the source sequence is null or undefined when invoke via call/apply/bind; or predicate is a generator function or not a function.

Param	Description
predicate	A function to test each element for a condition.

Example

const seq = Seq.of(1, 2, 42, 323, 423, 32, 23, 10, 11);
console.log(seq.findBack(x => x % 2 === 0));
// => 10

forall(predicate) ⇒ Seq

Tests if all elements of the sequence satisfy the given predicate.

Returns: boolean - true if the callback function returns a truthy value for at least one element in the sequence. Otherwise, false.
Throws:

• If the source sequence is null or undefined; or predicate is a generator function or not a function.

Param	Type	Description
predicate	function	A function to test on the elements of the seq.

Example

const seq = Seq.of(2, 4, 5, 8);
const result = seq.exists(x => x % 2 === 0);
console.log(result);
// => true

Seq.from(source) ⇒ Seq

Create a new sequence wrapped a given source. The given source can be anything that implemented iterable protocol.

Returns: Seq - The return sequence.
Throws:

• TypeError if source doesn't conform iterable protocol.

Param	Description
source	Anything that implemented iterable protocol.

Returns the first element of the sequence.

Returns: The first element of the sequence.
Example

@exception {TypeError} If the source sequence is null or undefined when invoke via call/apply/bind.
const seq = Seq.of(1, 2, 3, 4, 5);
console.log(seq.head());
// => 1

init(count, initializer) ⇒ Seq

Generate a new sequence by invoking initializer function passed as the argument up to the given count.

Returns: Seq - The result sequence.
Throws:

• TypeError if count is a negative number; or initializer is a generator function or not a function.

Param	Type	Description
count	Number	The maximum number of items to generate for the sequence.
initializer	function	A function that generates an item in the sequence from a given index.

Example

const fiveNums = Seq.init(5, x => x * 2);
console.log(fiveNums.toArray());
// => [0, 2, 4, 6, 8]

initInfinite(initializer) ⇒ Seq

Generate a new sequence by invoking initializer function passed as the argument. The index of the item generated is passed to the initializer function. The iteration can continue up to Number.MAX_SAFE_INTEGER.

Returns: Seq - The result sequence.
Throws:

• TypeError if initializer a generator function or not a function.

Param	Type	Description
initializer	function	A function that generates an item in the sequence from a given index.

Example

const seq = Seq.initInfinite(x => x * 2);
const first5Nums = seq.take(5);
console.log(first5Nums.toArray());
// => [0, 2, 4, 6, 8]

isEmpty() ⇒ Boolean

Returns true if the sequence contains no elements, false otherwise.

Returns: boolean - True if the sequence is empty; false otherwise.
Throws:

• TypeError if the existing sequence is null or undefined when invoke via call/apply/bind.

Example

console.log(Seq.empty().isEmpty());
// => true

iter(callback) ⇒ undefined

Applies the given function to each element of the collection.

Throws:

• TypeError If the source sequence is null or undefined when invoke via call/apply/bind; or predicate is a generator function or not a function.

Param	Type	Description
callback	function	A function to apply to each element of the sequence.

Example

const seq = Seq.of(1, 2, 3, 4, 5);
seq.iter(x => console.log(x));
// =>   1
// =>   2
// =>   3
// =>   4
// =>   5

last() ⇒ value

Returns the last element of a sequence.

Returns: The value at the last position in the source sequence.
Throws:

• TypeError If the source sequence is null or undefined when invoke via call/apply/bind.

Example

const seq = Seq.range(0,10);
const last = seq.last();
console.log(last);
// => 9

length ⇒ Number

Returns the length of the sequence.

Returns: number - The length of the sequence.
Throws:

• TypeError if the existing sequence is null or undefined when invoke via call/apply/bind.

Example

const seq = Seq.of(1,2,3);
console.log(seq.length);
// => 3;

map(callback) ⇒ Seq

The map method creates a new Seq populated with the results of calling a provided function on forall element. The provided function is invoked with two arguments: (item, index).

Returns: Seq - Return the new mapped sequence.
Throws:

• TypeError If the source sequence is null or undefined when invoke via call/apply/bind; or callback is a generator function or not a function.

Param	Type	Description
callback	function	The function invoked on each item.

Example

const seq = Seq.of(1,2,3,4,5).map(x => x * x);
console.log([...seq]);
// => [1, 4, 9, 16, 25]

const seq = Seq.of(1,2,3,4,5).map((item, index) => [index, item]);
console.log([...seq]);
// => [[0, 1], [1, 2], [2, 3], [3, 4], [4, 5]]

Seq.of(elem0[elem1[,...[,elemN]]]) ⇒ Seq

Creates a new sequence from a variable number of arguments, regardless of number or type of the arguments.

Returns: Seq - A new sequence.

Param	Description
args	Elements used to create the sequence.

Example

const nums = Seq.of(1,2, { 'three' : 3}, [4], '5', 0b110);
console.log(nums);
// => [ 1, 2, { three: 3 }, [ 4 ], '5', 6 ]

prepend([val1[,val2[,...[,valN]]]]) ⇒ Seq

Creates a new sequence with new values prepended.

Returns: Seq - A new sequence.
Throws:

• TypeError if the existing sequence is null or undefined when invoke via call/apply/bind.

Param	Description
...others	Iterable, iterator, generator function, array-like object, or single value to prepend into new sequence. If omitted, the method returns the existing sequence.

Example

const seq = Seq.of(4,5);
const prepended = seq.prepend([1,2], { three : 3 });
console.log(prepended.toArray());
// => [ 1, 2, { three: 3 }, 4, 5]

Seq.range(begin, end, step) ⇒ Seq

Creates a sequence of numbers starting from 'begin' to 'end', but not including, 'end'. If 'end' is not defined, it is set to 'begin', and 'begin' is then set to 0. 'step' will be assigned to -1 if 'begin' is negative and 'end' is not defined.

Returns: Seq - The result sequence.
Throws:

• TypeError if 'begin', 'end', and 'step' are not finite numbers when passed.

Param	Type	Default	Description
[begin]	number	0	The first number of the sequence
end	number		The end of the range of numbers. It won't include in the result sequence.
[step]	number	1	The value to increment or decrement by.

Example

console.log(Seq.range(5).toArray());
// => [ 0, 1, 2, 3, 4 ]

console.log(Seq.range(-5).toArray());
// => [ 0, -1, -2, -3, -4 ]

console.log(Seq.range(1,5).toArray());
// => [ 1, 2, 3, 4 ]

console.log(Seq.range(0, 20, 5).toArray());
// => [ 0, 5, 10, 15 ]

console.log(Seq.range(0, -5, -1).toArray());
// => [ 0, -1, -2, -3, -4 ]

console.log(Seq.range(0).toArray());
// => []

console.log(Seq.range(10, -5, -1).toArray());
// => [ 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0, -1, -2, -3, -4 ]

console.log(Seq.range(-1, -2, -5).toArray());
// => [-1]

reduce(reducer) ⇒ Any

The method executes the provided reducer function on each element of the sequence, resulting in single output value.

Returns: A single value that results from reduction.
Throws:

• TypeError If the source sequence is null or undefined when invoke via call/apply/bind; or reducer is a generator function or not a function; or when the source sequence is empty and initial value is not provided.

Param	Type	Description
reducer	function	It takes two arguments - (accumulator, currentValue). if initialValue is provided, the value will be used as the first argument in the reducer. Otherwise; the first element of the sequence will be used as the first argument.

Example

const result = Seq.of(1, 2, 3, 4, 5, 6, 7, 8, 9, 10).reduce((accumulator, currentValue) => accumulator + currentValue);
console.log(result);
// => 55

const result = Seq.of([0, 1], [2, 3], [4, 5]).reduce((accumulator, currentValue) => accumulator.append(currentValue) , []);
console.log(result);
// => [0, 1, 2, 3, 4, 5]

replicate(count, initial) ⇒ Seq

Creates a sequence by replicating the given initial value.

Returns: Seq - The generated sequence.
Throws:

• TypeError if count is a negative number.

Param	Type	Description
count	Number	The number of elements to replicate.
initial		The value to replicate.

Example

const seq = Seq.replicate(5, 1);
console.log(seq.toArray());
// => [1, 1, 1, 1, 1]

reverse() ⇒ Seq

Return a new sequence with the elements in reverse order.

Returns: Seq - The reversed sequence.
Throws:

• TypeError if the source sequence is null or undefined when invoke via call/apply/bind.

Example

const seq = Seq.of(0, 1, 2, 3, 4);
console.log(seq.reverse().toArray());
// => [4, 3, 2, 1, 0]

Returns a new sequence containing all the elements of the existing sequence except the first.

Returns: Seq - The result sequence.
Example

@exception {TypeError} If the source sequence is null or undefined when invoke via call/apply/bind.
const seq = Seq.of(1, 2, 3, 4, 5);
console.log(seq.tail().toArray());
// => [2, 3, 4, 5]

take(count) ⇒ Seq

Returns the first N elements of the sequence.

Returns: Seq - The result sequence.
Throws:

• TypeError if the source sequence is null or undefined when invoke via call/apply/bind; or count is a negative number.

Param	Description
count	The number of items to take.

Example

const seq = Seq.of(1,2,3,4,5);
const taken = seq.take(2);
console.log([...taken]);
// => [1, 2]

takeWhile(predicate) ⇒ Seq

Returns a sequence that, when iterated, yields elements of the underlying sequence while the given predicate returns True, and then returns no further elements.

Returns: Seq - The result sequence.
Throws:

• TypeError If the source sequence is null or undefined when invoke via call/apply/bind; or predicate is a generator function or not a function.

Param	Type	Description
predicate	function	A function that evaluates to false when no more items should be returned.

Example

const seq = Seq.from([1, 2, 3, 1, 2, 3]);
const result = seq.takeWhile(x => x < 3).toArray();
console.log(result);
=> [1, 2]

toArray() ⇒ Seq

Create an array out of the sequence.

Returns: Array - The result array.
Throws:

• TypeError if the existing sequence is null or undefined when invoke via call/apply/bind.

Example

const seq = Seq.of(1,2,3,4);
const arr = seq.toArray();
console.log(arr);
// => [1,2,3,4]

toString() ⇒ string

Returns a string representing upto 128 elements of the sequence. If the sequence contains more than 128 elements, the string will end with '...'.

Returns: A string representing the elements of the sequence.
Throws:

• TypeError If the source sequence is null or undefined when invoke via call/apply/bind.

Example

console.log(Seq.of(1,2,3).toString());
// => "1, 2, 3"