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Range with Generator Function

Published at25 Jul 2026
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JavaScript Functions Hard 0 views
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Write a JavaScript generator function that takes a start and end value, yields each integer in that range, and returns the values as an array. Use the function* syntax with yield to produce values lazily.

Generator functions in JavaScript are defined with function* syntax and use the yield keyword to pause and resume execution. Each call to the generator's .next() method executes until the next yield statement, returning an object { value, done }. Generator functions can produce infinite sequences lazily because values are computed only when requested.

Generators are a powerful JavaScript feature for lazy evaluation, custom iteration, and managing asynchronous flow. They implement the iterator protocol (Symbol.iterator) and can be used with for-of loops and spread operators. The Array.from() method can consume a generator to produce an array: Array.from(gen()).

Time complexity is O(n) for consuming all yielded values, where n is the range size. Each yield pauses and resumes the generator function. Space complexity is O(1) for the generator state, O(n) for the collected array.

Edge cases include empty ranges (start >= end, generator yields nothing), single-element ranges, negative values, and ensuring the generator correctly handles the inclusive start and exclusive end convention.

Example Input & Output

Example 1
Input
0,3
Output
[0,1,2]
Explanation

Range 0 to 2

Example 2
Input
5,5
Output
[]
Explanation

Empty range (start equals end)

Example 3
Input
1,5
Output
[1,2,3,4]
Explanation

Range 1 to 4

Example 4
Input
10,13
Output
[10,11,12]
Explanation

Three elements

Example 5
Input
-2,2
Output
[-2,-1,0,1]
Explanation

Negative to positive

Algorithm Flow

Recommendation Algorithm Flow for Range with Generator Function
Recommendation Algorithm Flow for Range with Generator Function

Solution Approach

function* range(start, end) {
  for (var i = start; i < end; i++) {
    yield i;
  }
}

function solution(start, end) {
  return Array.from(range(start, end));
}

Best Answers

javascript - Approach 1
function* range(start, end) {
  for (var i = start; i < end; i++) {
    yield i;
  }
}

function solution(start, end) {
  return Array.from(range(start, end));
}