Add a configuration option to CodeMirror called "noNewlines" that when set as true
will prevent any newline characters from being typed into the CodeMirror editor and any newline character pasted into the editor will be replaced by a single space.
var myCodeMirror = CodeMirror(document.body, {
value: "function myScript(){return 100;}\n",
mode: "javascript",
noNewlines: true
});
Significant inspiration from https://discuss.codemirror.net/t/single-line-codemirror/195/4