monaco-editor/website/playground/new-samples/extending-language-services/codelens-provider-example/sample.js

var editor = monaco.editor.create(document.getElementById("container"), {
    value: "{\n\t\"dependencies\": {\n\t\t\n\t}\n}\n",
    language: "json"
});

var commandId = editor.addCommand(0, function() {
    // services available in `ctx`
    alert('my command is executing!');

}, '');

monaco.languages.registerCodeLensProvider('json', {
    provideCodeLenses: function(model, token) {
        return [
            {
                range: {
                    startLineNumber: 1,
                    startColumn: 1,
                    endLineNumber: 2,
                    endColumn: 1
                },
                id: "First Line",
                command: {
                    id: commandId,
                    title: "First Line"
                }
            }
        ];
    },
    resolveCodeLens: function(model, codeLens, token) {
        return codeLens;
    }
});