Getting MathJax to update after changes to Angular

Question

I am trying to use AngularJS two-way binding text which includes Latex style equations. I would like to call MathJax to format the equations, but I'm not sure of the best way to ensure that MathJax is called after AngularJS finishes changing the model. I think I need a callback. Here is my JavaScript:

var myApp = angular.module('myApp',[]);
function MyCtrl($scope) {
   $scope.Update = function() {
       $scope.Expression = 'Evaluate: \\( \\frac{9}{4} \\div \\frac{1}{6} \\)';
       MathJax.Hub.Queue(["Typeset", MathJax.Hub]);
   }
   $scope.Expression = 'Evaluate: \\( \\frac{5}{4} \\div \\frac{1}{6} \\)';

}

And here is my HTML:

<div ng-controller="MyCtrl">
    <button ng-click="Update()">Update</button>
  {{Expression}}
</div>

Fiddle is here: http://jsfiddle.net/LukasHalim/UVjTD/1/. You'll notice that on the fiddle the original expression isn't removed even after you click the update button twice - seems like a bug or conflict.

Answer 1

Here's a directive that lets you use double curly markup inside the expression (and doesn't require setting an expression variable on the scope). It's based on this blog post, except I only support MathJax, and I save the compiled DOM, so that it updates on changes to scope variables.

As Alex Osborn said, it's best to separate non-math from math.

Usage:

<p>This is inline math: <latex>x^{ {{power}} }</latex>, 
and this is display math: <div latex> y^{ {{power}} } .</div></p>

In a snippet:

angular.module('app', [])
  .controller('ctrl', function($scope) {
    $scope.power = "\\sin(x^2)";
  })
  .directive('latex', function() {
    return {
      restrict: 'AE',
      link: function(scope, element) {
        var newDom = element.clone();
        element.replaceWith(newDom);
        var pre = "\\(",
          post = "\\)";
        if (element[0].tagName === 'DIV') {
          pre = "\\[";
          post = "\\]";
        }
        scope.$watch(function() {
          return element.html();
        }, function() {
          console.log(element);
          newDom.html(pre + element.html() + post);
          MathJax.Hub.Typeset(newDom[0]);
        });
      }
    }
  });

<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.23/angular.min.js"></script>
<script src="https://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-AMS-MML_HTMLorMML"></script>

<div ng-app="app" ng-controller="ctrl">
  <p>Power:
    <input ng-model="power" />
  </p>
  <p>This is the inline latex,
    <latex>x^{ {{power}} }</latex>, followed by some display mode latex
    <div latex>y^{ {{power}} } = {{power}}.</div>And that's it!
  </p>
</div>

Answer 2

You can try with my modifications http://jsfiddle.net/bmma8/4/ modify input or click on button will update your expression.

js:

MathJax.Hub.Config({
    extensions: ["tex2jax.js"],
    jax: ["input/TeX","output/HTML-CSS"],
    tex2jax: {inlineMath: [["$","$"],["\\(","\\)"]]}
});

var myApp = angular.module('myApp',[]);


function MyCtrl($scope, $log) {

    var QUEUE = MathJax.Hub.queue;  // shorthand for the queue

    $scope.Update = function() {
        QUEUE.Push(["Text",MathJax.Hub.getAllJax("MathOutput")[0],"\\displaystyle{"+ $scope.Expression+"}"]);
        //$scope.Expression = 'Updated Expression: \\( \\frac{9}{4} \\div \\frac{1}{6} \\)';
        //MathJax.Hub.Queue(["Typeset", MathJax.Hub]);
    }
    $scope.Expression = 'Original Expression: \\( \\frac{5}{4} \\div \\fra

and html:

 <div ng-controller="MyCtrl">
         <button ng-click="Update()">Update</button>

         <input ng-model="Expression" ng-change="Update()">
         <div id="MathOutput">
         You typed: ${}$
         </div>
 </div>

Alexandre

Answer 3

Simplest, fastest and most stable solution:

$rootScope.$watch(function(){
  MathJax.Hub.Queue(["Typeset",MathJax.Hub]);
  return true;
});

Advantages:

• Easy to setup, just copy this code.
• Everything on your page is typeset.
• It renders much faster than the other solutions. This is because it can render the page in one go. Other answers here wait for one item to finish, until they typeset the next one. That makes rendering veeeery slow if there are for example multiple mathjax-bind directives (as another answer suggests). This point is the reason I was looking for a different answer.
• You can still easily exclude elements using the option “ignoreClass” in your mathjax settings.

Benchmarking: 100 mathjax-bind directives took 63 seconds, while with this method it took 1.5 second to render the page. I know that this function will be executed a lot since it's called on every digest cycle, however, it doesn't noticeably slow down the page.

Answer 4

I actually thought of another solution. When you render some angular and math you do this:

ANGULAR CONTROLLER

$scope x = 5;

HTML

<h3> {{ '$ Multiplication = '+ x + ' * 2 =' + (x*2) + '$'}} </h3>

Formated Math Jax result

Multiplication = 5 * 2 = 10

The key is to include the dollar signs inside the brackets as text. When Angular renders them, the dollar signs will appear as plain text, but when the Math Jax format comes into action it will recognize the dollar signs and do the magic.

Answer 5

I fiddled a bit more on Roney's solution. The display math should be displayed in display mode; with

<script type="math/tex; mode=display">

I added an attribute to the generated span to indicate that.

Fiddle is here http://jsfiddle.net/repa/aheujhfq/8/

Answer 6

Having wasted many days (and maybe weeks) fighting MathJax, I'm all too familiar with its various quirks with updating math expressions on the fly. I'm brand new to Angular but this gave me a good chance to dive in and I ended up with a solution which solves my problems -- hopefully it'll solve yours as well.

Live demo: jsfiddle

---

Instead of using the plain interpolation that Angular provides, I created a new directive based on ng-bind called mathjax-bind.

If expression is a variable containing math code, then instead of \( {{expression}} \) you can write:

<span mathjax-bind="expression"></span>

and everything will be typeset and updated at the appropriate times.

The supporting code for the directive follows:

myApp.directive("mathjaxBind", function() {
    return {
        restrict: "A",
        controller: ["$scope", "$element", "$attrs",
                function($scope, $element, $attrs) {
            $scope.$watch($attrs.mathjaxBind, function(texExpression) {
                var texScript = angular.element("<script type='math/tex'>")
                    .html(texExpression ? texExpression :  "");
                $element.html("");
                $element.append(texScript);
                MathJax.Hub.Queue(["Reprocess", MathJax.Hub, $element[0]]);
            });
        }]
    };
});