[main] add promise API

Resolves pkra#19

Author: pkra

lib/main.js

@@ -133,12 +133,22 @@ const preprocessor = function (data, callback) {
 
 exports.start = mathjax.start;
 exports.config = mathjax.config;
-exports.typeset = function (data, callback) {
+const cbTypeset = function (data, callback) {
     if (data.enrich) {
         preprocessor(data, function (result) {
             main(result, callback);
         })
     } else main(data, callback);
 };
+// main API, callback and promise compatible
+exports.typeset = function (data, callback) {
+    if (callback) cbTypeset(data, callback);
+    else return new Promise(function (resolve, reject) {
+        cbTypeset(data, function (output, input) {
+            if (output.errors) reject(output.errors);
+            else resolve(output, input);
+        });
+    });
+};
 exports.postprocessor = postprocessor;
 exports.preprocessor = preprocessor;

test/base-typeset-promise.js

@@ -0,0 +1,22 @@
+var tape = require('tape');
+var mjsre = require("../lib/main.js");
+
+tape('Base: typeset promise API', function (t) {
+    t.plan(2);
+
+    var tex = '';
+    mjsre.start();
+
+    // promise resolved
+    mjsre.typeset({
+        math: tex,
+        format: "TeX",
+        mml: true
+    }).then((result) => t.ok(result.mml, 'Typset promise resolved on success'));
+
+    mjsre.typeset({
+        math: tex,
+        format: "MathML",
+        mml: true
+    }).catch((error) => t.ok(error, 'Typeset promise rejected on error'));
+});