monaco-editor/website/playground/new-samples/creating-the-diffeditor/hello-diff-world/sample.js

var originalModel = monaco.editor.createModel('heLLo world!', 'text/plain');
var modifiedModel = monaco.editor.createModel('hello orlando!', 'text/plain');

var diffEditor = monaco.editor.createDiffEditor(document.getElementById('container'));
diffEditor.setModel({
	original: originalModel,
	modified: modifiedModel
});