fix: use a semaphore to avoid running axe concurrently (#33)

A previous commit (1d4bd8d) removed our pseudo-semaphore which prevented us from running aXe concurrently. This patch adds back our "timer" semaphore and ensures we do not can `axe.run()` more than once on the same tick.

Closes #32.

index.js

@@ -11,6 +11,8 @@ var moderate = 'color:orange;font-weight:bold;';
 var minor = 'color:orange;font-weight:normal;';
 var defaultReset = 'font-color:black;font-weight:normal;';
 
+var timer;
+var timeout;
 var _createElement;
 var components = {};
 var nodes = [];
@@ -92,16 +94,37 @@ function failureSummary(node, key) {
 	}
 }
 
-function checkAndReport(node) {
+function createDeferred () {
+	var deferred = {};
+
+	deferred.promise = new Promise(function (resolve, reject) {
+		deferred.resolve= resolve
+		deferred.reject = reject
+	})
+
+	return deferred;
+}
+
+function checkAndReport(node, timeout) {
+	if (timer) {
+		clearTimeout(timer);
+		timer = undefined;
+	}
+
+	var deferred = createDeferred()
+
 	nodes.push(node);
-	return new Promise(function(res, rej) {
+	timer = setTimeout(function () {
 		var n = getCommonParent(nodes);
 		if (n.nodeName.toLowerCase() === 'html') {
 			// if the only common parent is the body, then analyze the whole page
 			n = document;
 		}
 		axeCore.run(n, { reporter: 'v2' }, function (error, results) {
-			if (error) { throw rej(error); }
+			if (error) {
+				return deferred.reject(error)
+			}
+
 			results.violations = results.violations.filter(function (result) {
 				result.nodes = result.nodes.filter(function (node) {
 					var key = node.target.toString() + result.id;
@@ -141,16 +164,19 @@ function checkAndReport(node) {
 				});
 				console.groupEnd();
 			}
-			res();
+
+			deferred.resolve()
 		});
-	});
+	}, timeout);
+
+	return deferred.promise;
 }
 
 function checkNode(component) {
 	var node = ReactDOM.findDOMNode(component);
 
 	if (node) {
-		checkAndReport(node);
+		checkAndReport(node, timeout);
 	}
 }
 
@@ -166,9 +192,10 @@ function addComponent(component) {
 	}
 }
 
-var reactAxe = function reactAxe(_React, _ReactDOM, conf) {
+var reactAxe = function reactAxe(_React, _ReactDOM, _timeout, conf) {
 	React = _React;
 	ReactDOM = _ReactDOM;
+	timeout = _timeout;
 
 	if (conf) {
 		axeCore.configure(conf);
@@ -198,7 +225,7 @@ var reactAxe = function reactAxe(_React, _ReactDOM, conf) {
 		};
 	}
 
-	return checkAndReport(document.body);
+	return checkAndReport(document.body, timeout);
 };
 
 module.exports = reactAxe;