@extra-array/count-as/index.js

Counts occurrences of values.

'use strict';
function id(v) {
    return v;
}
function countAs(x, fm = null) {
    var fm = fm || id;
    var a = new Map(), i = -1;
    for (var v of x) {
        var v1 = fm(v, ++i, x);
        a.set(v1, (a.get(v1) || 0) + 1);
    }
    return a;
}
module.exports = countAs;