function findAllOccurrences(arr, target) {
    var a = []
    arr.forEach(function(item, index) {
        if(item === target) {
            a.push(index)
        }
    })
    return a
}

function findAllOccurrences(arr, target) {
    var result = []
    arr.filter(function(elem, index) {
        return target === elem && result.push(index)
    })
    return result
}