Javascript 如何定义此函数中的参数

Question

I am very new to Javascript and I am trying to figure out how array iteration works. In this code below, could somebody please explain to me how Javascript understands what the arguments in the function relate to -namely: value, index,array. Are these reserved keywords. If 'value', swapped positions inside the parantheses with 'index' would the function still work? Maybe i'm asking how or where have these arguments been defined?

    var txt ="";
    var numbers =[45,4,56,8, 32];
    numbers.foreach(myFunction);

    function myFunction (value,index,array) {
    txt= txt + value + "<br>";
    }

Answer 1

You can define your function parameters in Two Ways

1. Positional

In positional it does not matter what is the name of your parameters because parameters are assigned by their position not by their name so you can change myFunction(value, index, array) to myFunction(a, b, c) and It still works because their positions matters not their name.

2. Named

There is another way to defined function parameters where the position does not matter but naming them does.

For example a subtract function can be defined in two ways

function subtract({ firstNumber, secondNumber } = {}) {
  return firstNumber - secondNumber;
} 

which is Named and can be called with both subtract({ firstNumber: 10, secondNumber: 5 }) and subtract({ secondNumber: 5, firstNumber: 10 }) and still both results are the same but you have to remember the names.

But if defined in Positional :

function subtract(firstNumber, secondNumber) {
  return firstNumber - secondNumber;
} 

The two subtract(5, 10) and subtract(10, 5) yields different results because their position matters.