extension.js

// The module 'vscode' contains the VS Code extensibility API
// Import the module and reference it with the alias vscode in your code below
const vscode = require('vscode');
const flattenDeep = require('lodash/flattenDeep');
const ruleArray = require('./ruleArray.json');

function insertText(text) {
    var editor = vscode.window.activeTextEditor;
    editor.edit(function (editBuilder) {
        editBuilder.delete(editor.selection);
    }).then(function () {
        editor.edit(function (editBuilder) {
            editBuilder.insert(editor.selection.start, text);
        });
    });
}

// this method is called when your extension is activated
// your extension is activated the very first time the command is executed
function activate(context) {

    // Use the console to output diagnostic information (console.log) and errors (console.error)
    // This line of code will only be executed once when your extension is activated
    console.log('Congratulations, your extension "atomic-css-search" is now active!');

    // The command has been defined in the package.json file
    // Now provide the implementation of the command with  registerCommand
    // The commandId parameter must match the command field in package.json
    let disposable = vscode.commands.registerCommand('extension.searchAtomic', function () {
        // The code you place here will be executed every time your command is executed

        vscode.window.showQuickPick(flattenDeep(ruleArray), {
            placeHolder: ''
        })
        .then(selected => {
            const selectedClass = selected.split(') ');
            const finalClass = `${selectedClass[0]}) `;
            insertText(finalClass);
        });
    });

    context.subscriptions.push(disposable);
}
exports.activate = activate;

// this method is called when your extension is deactivated
function deactivate() {
}
exports.deactivate = deactivate;