Add counter snippet

test/counter/counter.js

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+const counter = (selector, start, end, step = 1, duration = 2000) => {
+let current = start,
+_step = (end - start) * step < 0 ? -step : step,
+timer = setInterval(() => {
+current += _step;
+document.querySelector(selector).innerHTML = current;
+if (current >= end) document.querySelector(selector).innerHTML = end;
+if (current >= end) clearInterval(timer);
+}, Math.abs(Math.floor(duration / (end - start))));
+return timer;
+};
+module.exports = counter;

test/counter/counter.test.js

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+const test = require('tape');
+const counter = require('./counter.js');
+
+test('Testing counter', (t) => {
+  //For more information on all the methods supported by tape
+  //Please go to https://github.com/substack/tape
+  t.true(typeof counter === 'function', 'counter is a Function');
+  //t.deepEqual(counter(args..), 'Expected');
+  //t.equal(counter(args..), 'Expected');
+  //t.false(counter(args..), 'Expected');
+  //t.throws(counter(args..), 'Expected');
+  t.end();
+});