Closures in JavaScript

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examples/js/create_incrementer.js

"use strict";

function create_incrementer(n) {
    return function (k) {
        return k+n;
    }
}

var inc_19 = create_incrementer(19);
var inc_17 = create_incrementer(17);
console.log(inc_19(23));  // 42
console.log(inc_17(23));  // 40

examples/js/create_counter.js

"use strict";

function create_counter(start, step) {
    var n;
    return function () {
        if (n === undefined) {
            n = start;
            return n;
        }
        n += step;
        return n;
    }
}

var count_by_3 = create_counter(1, 3);
var count_by_7 = create_counter(2, 7);

console.log(count_by_3());  // 1
console.log(count_by_3());  // 4
console.log(count_by_3());  // 7
console.log(count_by_7());  // 2
console.log(count_by_7());  // 9
console.log(count_by_7());  // 16
console.log(count_by_3());  // 10
console.log(count_by_7());  // 23