Function updateTextNode

lib/assets/react-source/development/react.js:17242–17254

(returnFiber, current, textContent, expirationTime)

	  }

	  function updateTextNode(returnFiber, current, textContent, expirationTime) {
	    if (current === null || current.tag !== HostText) {
	      // Insert
	      var created = createFiberFromText(textContent, returnFiber.mode, expirationTime);
	      created.return = returnFiber;
	      return created;
	    } else {
	      // Update
	      var existing = useFiber(current, textContent);
	      existing.return = returnFiber;
	      return existing;
	    }
	  }

	  function updateElement(returnFiber, current, element, expirationTime) {
	    if (current !== null) {