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Trick get a new copy of object/array using spread operator #1823

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@wonderingabout
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@wonderingabout wonderingabout commented Mar 26, 2020

A common trick using the spread operator :)
Credit goes to @Dorus for teaching me this trick !

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CLAassistant commented Mar 26, 2020 •
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@wonderingabout wonderingabout changed the title (削除) Trick deep copy spread (削除ここまで) (追記) Trick get a new copy of object/array using spread operator (追記ここまで) Mar 26, 2020

As we remember, arrow functions don't have their own `this`. Now we know they don't have the special `arguments` object either.
````
```
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Should not change this. It corresponds to the symbol on line 107.

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@wonderingabout wonderingabout Mar 27, 2020

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indeed, fixed


## Get a new copy of an object/array

Remember when we talked about `Object.assign()`
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Line 230 and 231 should be in one line?

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@wonderingabout wonderingabout Mar 27, 2020

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generally, github formatting does automatically a word wrap for one skipped line, the purpose was to keep easy to read code in the github editor
the javascript.info may not behave the same way, so i fixed it to one long line

## Get a new copy of an object/array

Remember when we talked about `Object.assign()`
[in the past](https://javascript.info/symbol#symbols-are-skipped-by-for-in) ?
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Suggested change
[in the past](https://javascript.info/symbol#symbols-are-skipped-by-for-in)?
[in the past](https://javascript.info/symbol#symbols-are-skipped-by-for-in)?

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@wonderingabout wonderingabout Mar 27, 2020

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fixed, thanks

Remember when we talked about `Object.assign()`
[in the past](https://javascript.info/symbol#symbols-are-skipped-by-for-in) ?

It is possible to do the exact same thing with the spread operator !
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It is possible to do the exact same thing with the spread operator!
It is possible to do the exact same thing with the spread operator!

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@wonderingabout wonderingabout Mar 27, 2020

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fixed, thanks

let arrCopy = [...arr]; // spread the array into a list of parameters
// then put the result into a new array
// do the arrays have the exact same contents ?
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// do the arrays have the exact same contents?
// do the arrays have the exact same contents?

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@wonderingabout wonderingabout Mar 27, 2020

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fixed, thanks

// do the arrays have the exact same contents ?
alert(JSON.stringify(arr) === JSON.stringify(arrCopy)); // true (same content)
// are the arrays equal (they share the same reference) ?
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// are the arrays equal (they share the same reference)?
// are the arrays equal (they share the same reference)?

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@wonderingabout wonderingabout Mar 27, 2020

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fixed, thanks

alert(arrCopy) // 1, 2, 3
```

Note that it is possible to do the exact same to copy
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Line 252 and 253 should be in one line?

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@wonderingabout wonderingabout Mar 29, 2020

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same as #1823 (comment)

// do the objects have the exact same contents ?
alert(JSON.stringify(obj) === JSON.stringify(objCopy)); // true (same content)
// are the arrays equal (they share the same reference) ?
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Suggested change
// are the arrays equal (they share the same reference)?
// are the arrays equal (they share the same reference)?

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@wonderingabout wonderingabout Mar 27, 2020

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fixed, thanks

alert(obj === objCopy); // false (not same reference)
```

This way of copying an object is much shorter than
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Line 267 and 268 should be in one line?

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@wonderingabout wonderingabout Mar 27, 2020

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same as #1823 (comment)

@wonderingabout wonderingabout force-pushed the trick-deep-copy-spread branch 2 times, most recently from 0c158d9 to a54f242 Compare March 27, 2020 06:51
@lex111 lex111 requested a review from paroche March 29, 2020 03:00
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paroche commented Mar 29, 2020

Alexey -- is there a specific change you want me to look at? Everything I see above seems to be marked "outdated".

In the a54f242 branch linked to in the last section there is some awkward language:

'Note that it is possible to do the exact same to copy of objects: '

could be improved:

'Note that it is possible to do the exact same thing to copy objects:'

or

'Note that it is possible to do the exact same thing to make a copy of an object:'
(my preference)

Rest of the language is OK.

Anything else?

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wonderingabout commented Mar 29, 2020 •
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fixed, it's indeed clearer

i removed the unneeded "exact" word :

'Note that it is possible to do the same thing to make a copy of an object:'

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paroche commented Mar 29, 2020

Fine by me!

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@paroche did you accidentally hit the close PR instead of the merge PR button (just asking myself 🤔 )

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paroche commented Mar 29, 2020

You could say that. Anyway, as far as I'm concerned it should be merged (and closed).

@paroche paroche reopened this Mar 29, 2020
@paroche paroche merged commit c038ef4 into javascript-tutorial:master Mar 29, 2020
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paroche commented Mar 29, 2020 •
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And it is.

Not sure if it was my place, but if not, it can be undone.

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yes, you can always @ me if we need to change something

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