2631. Group By

https://leetcode.com/problems/group-by

Javascript

Array.prototype.groupBy = function(fn) {
    const groups = {}
    this.forEach((value) => {
        const key = fn(value)
        if (!groups.hasOwnProperty(key)) {
            groups[key] = []
        }
        groups[key].push(value)
    })
    return groups
};

Typescript

declare global {
    interface Array<T> {
        groupBy(fn: (item: T) => string): Record<string, T[]>
    }
}

Array.prototype.groupBy = function(fn) {
    const groups = {}
    this.forEach((value) => {
        const key = fn(value)
        if (!groups.hasOwnProperty(key)) {
            groups[key] = []
        }
        groups[key].push(value)
    })
    return groups
}