Question 331019 in Javascript Question posted in
A very good W3school tutorial can be found here.

Javascript – Providing seperate ref attribute to multiple element in reacJS

I am trying to build a simple to-do list where each task can be edited by clicking on edit button which shows a previously hidden text field in which user can enter new name for the current task, for this I need to assign a ref value to each task so far I have tried

   let refrences = useRef([]);               
   //this is within a array.map method
   <input type='text' ref={refrences.current[index]}  /> 
   //some code here

But refrences.current[index] always shows as undefined and I have no idea why that’s the case but when I try the following(found it online)

   let refrences = useRef([]);  
   //this is within a array.map method                  
   <input type='text' ref={element => refrences.current[index]=element}  /> 
   //some code here

This works perfectly fine but I have no idea why this works. I know this is an arrow function but I can’t tell what the ‘element’ stands for even though it has not been defined anywhere else. Any help would be appreciated

Tags:

2

Answers


  1. 0

    This works perfectly fine but I have no idea why this works.

    To the best of my knowledge you can pass at least two kinds of values to the ref pop:

    1. A "reference object" returned by useRef React Docs
    2. A function React Docs

    Reference object

    As you already know, useRef returns an object with a current property. When you pass that object to the ref prop, React can assign the DOM element to that property, i.e. something like

    ref.current = element

    (to be honest I don’t know if React requires the current property to be present. It might as well always assign to the current property if the passed value is an object)

    Function

    If you pass a function however, React will call that function with the DOM element passed as argument, something like:

    ref(element)

    I can’t tell what the ‘element’ stands for even though it has not been defined anywhere else.

    In your code element is a parameter of the function you pass to ref. It works like any other (callback) function. The caller of the function, in this case React, will provide a value for that argument.
    It’s essentially the same as for example Array#forEach and other higher level functions:

    [1, 2, 3].forEach(i => console.log(i))

    In this example you pass a function to forEach that has a single parameter i. The JavaScript engine will call that function for every element in the array and pass that element to the function (which therefore gets assigned to the parameter i).

    Why does ref={refrences.current[index]} not work?

    The value of reference.current[index] is not a "reference object". It’s not an object with a current property, so React cannot execute ref.current = element

    Login or Signup to reply.
  2. 0

    in fact, known as "using callback refs"
    by passing a callback to the ref, you get more granular control on binding a DOM element to the react ref object.
    you provide a callback and your current element which you have added ref props on it will be pass as element argument by react,

    so if you have an index, you know which position of reference array it should be placed and you also have a DOM reference using Element so you could capture it on your loop.

    Login or Signup to reply.
Please signup or login to give your own answer.

Back To Top
Search