Support arrow functions without a block statement

lib/js-yaml/type/js/function.js

@@ -65,8 +65,14 @@ function constructJavascriptFunction(data) {
 
   // Esprima's ranges include the first '{' and the last '}' characters on
   // function expressions. So cut them out.
+  if (ast.body[0].expression.body.type === 'BlockStatement') {
+    /*eslint-disable no-new-func*/
+    return new Function(params, source.slice(body[0] + 1, body[1] - 1));
+  }
+  // ES6 arrow functions can omit the BlockStatement. In that case, just return
+  // the body.
   /*eslint-disable no-new-func*/
-  return new Function(params, source.slice(body[0] + 1, body[1] - 1));
+  return new Function(params, 'return ' + source.slice(body[0], body[1]));
 }
 
 function representJavascriptFunction(object /*, style*/) {

test/samples-common/construct-javascript-function.js

@@ -31,6 +31,9 @@ testHandler.expected = [
   function () {
     return 72;
   },
+  function () {
+    return 23;
+  },
   function (x, y) {
     return x + y;
   },

test/samples-common/construct-javascript-function.yml

@@ -1,5 +1,6 @@
 - !!js/function 'function () { return 42 }'
 - !!js/function '() => { return 72 }'
+- !!js/function '() => 23'
 - !!js/function 'function (x, y) { return x + y; } '
 - !!js/function |
   function (foo) {