MathJax typesets removed DOM elements causing measureTextNodeWithCache pollution

Issue Summary

In MathJax 4.0.0.beta7, due to some asynchronous execution issues, I sometimes call typeset on the element after the element is removed.

Some of my CJK characters are folded together. I looked at the source code and it was roughly due to the following reasons.

When Mathjax (svg) encounters a cjk character, it calls jax.unknownText to create a text element, and then calls jax.measureTextNodeWithCache to calculate the text width (or read the cache)

If the dom is removed, the em/ex value calculated by Metrics will be NaN, which will cause the element created by jax.unknownText to get fontsize:NaNpx, and measureTextNodeWithCache will get a value close to 0.

So far, everything is fine, because the rendering result will not actually be on window, but measureTextNodeWithCache will record the calculation result in a persistent cache, which will eventually cause all subsequent width calculations of this CJK character to fail.

Steps to Reproduce:

const mathjax = await getMathJax();
const div1 = document.createElement('div');
div1.innerText = '\\(\\ce{ZnCO3 \\xlongequal{高温} ZnO + CO2 ^}\\)';
document.body.appendChild(div1);
const p = mathjax.typesetPromise([div1]);
div1.remove();
await p;
const div2 = document.createElement('div');
div2.innerText = '\\(\\ce{ZnCO3 \\xlongequal{高温} ZnO + CO2 ^}\\)';
document.body.appendChild(div2);
mathjax.typesetPromise([div2]);

Technical details:

• MathJax Version: 4.0.0.beta7
• Client OS: (e.g., Mac OS X 10.8.4)
• Browser: (e.g., Chrome 29.0.1547.57)