Clarification in the example of comma operator #3542
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| Please note that the comma operator has very low precedence, lower than `=`, so parentheses are important in the example above. | ||
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| 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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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
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| 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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a little more direct:
This is confusing because the
,operator should “evaluate each expression, but return the result of only the last one”.
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| 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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| 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 + 4evaluates+first, summing the numbers intoa = 3, 7, then the assignment operator=assignsa = 3, and the rest (, 7) is ignored. It's like(a = 1 + 2), 3 + 4.
to emphasize the evaluation of 3+4?
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Basic operators, maths
I think we need to add a clarification to this example, because if we run
a = 1 + 2, 3 + 4or(a = 1 + 2), 3 + 4in strict mode, we getReferenceError: a is not defined. I've seen several comments regarding this (some even tried to run this line of code withlet:let a = 1 + 2, 3 + 4)