Execute object's method from text input

MethodTextInterface.js

const object = {
            help: function () {
                console.log(`Object keys: ${Object.keys(this).filter(k => !k.includes('_')).join(', ')}`)
            },
            emit: function (payload) {
                console.log(payload.join(' '))
            },
            _private: function () {
                console.log('private')
            }
        }

        function MethodTextInterface() {
            let target = undefined
            const input = document.createElement('input')

            this.setTarget = function (targetObject) {
                if (typeof targetObject !== 'object') return
                target = targetObject
            }

            this.getDom = function () {
                return input
            }

            function handler(input, target) {
                if (!input || !target) return

                const words = input.split(' ')

                const firstWord = words[0]
                const isFirstWordPublic = firstWord.includes('_') === false
                const haveFirstWord = target[firstWord]
                const firstWordIsFunction = typeof target[firstWord] === 'function'

                if (haveFirstWord && isFirstWordPublic && firstWordIsFunction) {
                    const restWords = words.slice(1, words.length)

                    // execute target object's method, pass rest of the words
                    target[firstWord](restWords)
                }

                return { input, target }
            }

            input.placeholder = 'type "help"'
            input.onkeydown = function (e) {
                if (e.key === 'Enter') {
                    handler(this.value, target)
                }
            }

            return this
        }


        const game = {
            createElement: function (key) {
                let element
                if (key === 'method-text-interface') {
                    element = new MethodTextInterface()
                }
                return element
            }
        }

        const methodTextInterface = game.createElement('method-text-interface')
        methodTextInterface.setTarget(object)
        console.log(methodTextInterface)
        document.body.appendChild(methodTextInterface.getDom())