Sample Ace Editor custom completer

CustomCompleter.js

// fetch ace's language tools module:
var langTools = ace.require('ace/ext/language_tools');

// data stub:
var sqlTables = [
  { name: 'users', description: 'Users in the system' },
  { name: 'userGroups', description: 'User groups to which users belong' },
  { name: 'customers', description: 'Customer entries' },
  { name: 'companies', description: 'Legal entities of customers' },
  { name: 'loginLog', description: 'Log entries for user log-ins' },
  { name: 'products', description: 'Products offered in the system' },
  { name: 'productCategories', description: 'Different product categories' }
];

// create a completer object with a required callback function:
var sqlTablesCompleter = {
  getCompletions: function(editor, session, pos, prefix, callback) {
    callback(null, sqlTables.map(function(table) {
      return {
        caption: table.description,
	value: table.name,
	meta: "Table"
      };
    }));	
  }
};
// finally, bind to langTools:
langTools.addCompleter(sqlTablesCompleter);

For anyone curious how to set this only to work to autocomplete for SQL mode -

var sqlTablesCompleter = {
  getCompletions: function(editor, session, pos, prefix, callback) {
    // Check if the editor's session mode is SQL
    if (session.$mode && session.$mode.$id === 'ace/mode/sql') {
      callback(null, sqlTables.map(function(table) {
        return {
          caption: table.description,
          value: table.name,
          meta: "Table"
        };
      }));
    }
  }
};