JS arguments in a function with slice() return undefined

Question

I'm trying to pass two arguments in a function that has String.prototype.slice(), but the console keeps on returning this error:

Uncaught TypeError: Cannot read property 'slice' of undefined".

Aren't the arguments supposed to be passed?

 const testText = '<p style='color: red;'>This is a test</p>' const testParagraph = document.getElementById('test') const message = (paragraph, originText) => { let i = 0, text, isTag const speed = 50 text = originText.slice(0, ++i) if (text === originText) return paragraph.innerHTML = text const char = text.slice(-1) if (char === '<') isTag = true if (char === '>') isTag = false if (isTag) return message() setTimeout(message, speed) } message(testParagraph, testText)

 <div id="test"></div>

Answer 1

There are two places where a recursive call of message function may happen:

if (isTag) return message()
setTimeout(message, speed)

In both cases message function is called without arguments. Due to this paragraph are originText parameters are associated with undefined value. Then it tries to call .slice on undefined which raises the error.

You need to pass arguments to a recursive call, since it (like a regular function invocation) creates a new execution context with it's one lexical environment.

if (isTag) return message(arg1, arg2)
setTimeout(message.bind(null, arg1, arg2), speed)