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Clarification in the example of comma operator #3542

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Clarification in the example of comma operator #3542

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14 changes: 12 additions & 2 deletions 1-js/02-first-steps/08-operators/article.md
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Expand Up @@ -458,12 +458,22 @@ alert( a ); // 7 (the result of 3 + 4)

Here, the first expression `1 + 2` is evaluated and its result is thrown away. Then, `3 + 4` is evaluated and returned as the result.

```smart header="Comma has a very low precedence"
````smart header="Comma has a very low precedence"
Please note that the comma operator has very low precedence, lower than `=`, so parentheses are important in the example above.

Without them: `a = 1 + 2, 3 + 4` evaluates `+` first, summing the numbers into `a = 3, 7`, then the assignment operator `=` assigns `a = 3`, and the rest is ignored. It's like `(a = 1 + 2), 3 + 4`.
Try running the following code (**we don't use `"use strict"` in the example below, otherwise we would get an error**):
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@shallow-beach shallow-beach Aug 27, 2024 •
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simplify to use strict:

Try running the following code:

```js run
let a;
a = 1 + 2, 3 + 4;
alert(a); // 3
```

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not totally sure why doesn't work with inline declaration tbh. let modifies operation order somehow i guess? could be part of explanation


```js run no-strict
a = 1 + 2, 3 + 4;

alert(a); // 3
```

An unusual result, isn't it? Especially considering that the `,` operator should “evaluate each expression, but return the result of only the last one”.
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@shallow-beach shallow-beach Aug 27, 2024 •
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a little more direct:

This is confusing because the , operator should “evaluate each expression, but return the result of only the last one”.


Without them: `a = 1 + 2, 3 + 4` evaluates `+` first, summing the numbers into `a = 3, 7`, then the assignment operator `=` assigns `a = 3`, and the rest is ignored. It's like `(a = 1 + 2), 3 + 4`.
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maybe

Without parentheses, a = 1 + 2, 3 + 4 evaluates + first, summing the numbers into a = 3, 7, then the assignment operator = assigns a = 3, and the rest (, 7) is ignored. It's like (a = 1 + 2), 3 + 4.

to emphasize the evaluation of 3+4?

````

Why do we need an operator that throws away everything except the last expression?

Sometimes, people use it in more complex constructs to put several actions in one line.
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