intersect

function intersect<T>(...arrays: T[][]): T[];

Order comes from the first array, and the result is deduplicated: a value repeated there appears once. Values are compared with SameValueZero, the rule a Set uses, so NaN intersects with NaN — which a comparison by === never does — and -0 matches 0.

The arrays after the first each become a set once, and the first is then walked a single time. The cost is linear in the total input rather than the nested scan a hand-written version usually ends up being. The inputs are not modified.

Called with a single array, intersect returns its unique values; called with none, it returns [].

Parameters

Parameter	Type	Description
`...arrays`	`T[][]`	The arrays to intersect. Left untouched.

Returns

T[] — a new array of the shared values, in the order of the first array, without duplicates.

Throws

Exception	Condition
`TypeError`	Any argument is not an array.

Examples

Values shared by every array

intersect([1, 2, 3], [2, 3, 4]); // => [2, 3]
intersect([1, 2, 3], [2, 3], [3, 9]); // => [3]
intersect([1, 2], [9]); // => []

Finding the rows two sheets have in common

/**
 * Returns the identifiers that appear in both sheets, in the order of the
 * first one.
 */
export function findSharedIds(
  active: GoogleAppsScript.Spreadsheet.Sheet,
  billed: GoogleAppsScript.Spreadsheet.Sheet
): string[] {
  const left = active.getRange("A2:A").getValues().flat() as string[];

  const right = billed.getRange("A2:A").getValues().flat() as string[];

  return intersect(left, right);
}

function findSharedIds(active, billed) {
  const left = active.getRange("A2:A").getValues().flat();
  const right = billed.getRange("A2:A").getValues().flat();
  return intersect(left, right);
}

Deduplication and edge cases

intersect([1, 1, 2], [1, 2]); // => [1, 2] — the result is deduplicated
intersect([NaN], [NaN]); // => [NaN]
intersect([1, 2]); // => [1, 2] — a single array, deduplicated
intersect(); // => []

Source

src/lang/array/intersect.ts

23 September 2026

This documentation was generated with AI (Claude) from the library's source code.

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