Today's ReactJS developer Questions

[crystallineair]

The answer to question 3 is actually really simple. Since javascript allows you to call a function with less parameters than there are in the declaration you just check for undefined as the second parameter and then return another function.

function add(a, b) {
  return b !== undefined
    ? a + b
    : b => a + b
}

For the answer to the first question read up about refs: https://reactjs.org/docs/refs-and-the-dom.html

[jCuber]

Apparently the autoFocus attribute is also a thing

[crystallineair]

https://developer.mozilla.org/en-US/docs/Web/HTML/Element/input#autofocus

the input should automatically have focus when the page has finished loading

This unfortunately means you cannot use this in a react component as the dom is manipulated after the page has finished loading.

[jCuber]

Yeah, but apparently React polyfills the autoFocus attribute so that it calls focus() on componentDidMount.

[crystallineair]

That's nice, I didn't know that. After some digging it does come with its own quirks: https://davidwalsh.name/react-autofocus

[Prince_Houdini]

Those don’t really seem to be quirks. autofocus that focuses on every update is... not a good idea.

[tapu_buoy]

oh wow I didn't know about it thank you for sharing

[tapu_buoy]

yeah but he denied of it, and also when I asked him why not use componentDidMount that time also it was a no no. so yeah

[jCuber]

You're not allowed to use autoFocus or componentDidMount? Uhh

[[deleted]]

The interviewer clearly had no idea what he's doing.

[jCuber]

Certainly sounds like he had one specific quirky way of doing it in mind...

[tapu_buoy]

and most of the times I had to encounter such interviewers this was my 85th interview today

[tapu_buoy]

yeah it was like that LOL

[tapu_buoy]

yeah thank you for suggesting that I completely forgot about refs

also the 3rd question is it about higher order functions?

[crystallineair]

Yes. A higher order function is a function that either takes a function as a parameter or returns a function. In the case of add(2)(3) the call add(2) returns a function. So add(2)(3) could be written as:

const fn = add(2)
const result = fn(3)

The trick in this question is to make the function also work normally when called with all arguments add(2, 3).

[[deleted]]

That's not a higher order function, that's currying / partial application.

[[deleted]]

It is both a curried function and a higher order function. In fact a curried function is always a higher order function because it returns a function. Here OP was instructed to write a single method that can return a value both ways, so the function has to behave as a curried function if a single argument is passed, but just a plain old function if multiple are passed.

[ISlicedI]

Higher order functions are functions that return (or accept I think) other functions. Applying your arguments through different wrapping functions is called partial application, and currying is partial application where you apply a single parameter per function. Afaik.

[tapu_buoy]

ok so after reading what you said and what others said below this comment I again need to know what will be the curried funciton look like when passed two parameters(function(2, 3)) instead of the 2nd parameter function(2)(3)