Map.groupBy()
Map.groupBy() is a JavaScript method in the Map & Set category. Groups items into a Map by the callback key. The syntax is Map.groupBy(items, callbackFn). A typical example: Map.groupBy([1,2,3], n => n % 2) // Map {1 => [1,3], 0 => [2]}. A close sibling is Map.prototype.set(), which sets a key-value pair in the Map. A close sibling is Map.prototype.get(), which returns the value associated with a key. A close sibling is Map.prototype.has(), which checks if a key exists. A close sibling is Map.prototype.delete(), which removes a key-value pair. More about this category: Map and Set collection methods. Related Map & Set methods: Map.prototype.set(), Map.prototype.get(), Map.prototype.has(), Map.prototype.delete(), Map.prototype.clear(), Map.prototype.size, Map.prototype.keys(), Map.prototype.values(). This page is part of the free JS Reference documentation covering 1027+ methods, each with syntax, parameters, return values, examples, and common pitfalls. You can try Map.groupBy() immediately in the JavaScript playground, look up unfamiliar terms in the glossary, or return to the JS Reference homepage.