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  • Can't do push in forEach

Can't do push in forEach

# Emanuel Allen (10 years ago)

Surprise that I can't do arr1.forEeach(arr2.push);

Will throw an error.

Using bind as:

push = arr2.bind(push); arr1.forEeach(push);

Works... And not work. Seem to push individual elements and after every second element, it'll push the hold array.. And after and before each index that hold the array there are duplicate of that element preceding and following:

[1,2,array,2,3]//not this is with shift method [1,2,array,3,2]//note that this is with push

JS4L

# Garrett Smith (10 years ago)

On 5/14/15, Emanuel Allen <emanuelallen at hotmail.com> wrote:

Surprise that I can't do arr1.forEeach(arr2.push);

Check that line more carefully.

Will throw an error.

Using bind as:

push = arr2.bind(push);

Arrays don't have a bind method.

# Erik Arvidsson (10 years ago)

Still, the callback for forEach is called with 3 arguments; value, index and the array.

This is clearly documented in the spec and mdn and other resources.

# Emanuel Allen (10 years ago)

Meant the method of the array not the array m itself: array["push"&&"unshift"].bind(array);

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# Emanuel Allen (10 years ago)

Oh yes that is correct since push will push in elements separated by commas... Still my original problem is that I can't simply do arr.push(arr2.push); but it doesn't matter since it'll also push the three parameters into the array as well.

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# Allen Wirfs-Brock (10 years ago)

On May 14, 2015, at 8:19 AM, Emanuel Allen wrote:

Oh yes that is correct since push will push in elements separated by commas... Still my original problem is that I can't simply do arr.push(arr2.push); but it doesn't matter since it'll also push the three parameters into the array as well.

exactly, see www.wirfs-brock.com/allen/posts/166

# Emanuel Allen (10 years ago)

That would be great to have an only method on Function.prototype.only

It can take one to three parameters as arguments: -Only with using the first argument:

SomeFunction.only(1); only allow the first argument in. It target the place holder so: fn.only(2) allow the two most left argument in.

-Only with using the first 2 argument:

SomeFunction.only(1,2); only allow the second argument in; the second argument target where to start and the first not how many to let in. So fn.only(2,3); let the third and fourth argument in.

-Only with using all arguments placeholder:

SomeFunction.only(1,2,true); This will denote that we start from the right and and let the second from last argument in

The last parameter is informing if we should start left or right when choosing the parameters to let in. The default is false; start left to right

Internally this could use the function's arguments object to query what to let in.

JS4L

# Andrea Giammarchi (10 years ago)

$1 => a.push($1)

fat arrow function shines mostly in these cases, not sure there's a need for anything else.

($1, $2, $3) => a.push($2, $3)

# Emanuel Allen (10 years ago)

It should allow for:

arr.forEach(arr.push.only(1));//only return a function limiting the number of arguments pass to it...

But I guess this work too: arr.forEach(e=>arr.push(e));

But my goal was to just: arr.forEach(arr.push);//will not work

So this style I favorite since I want to avoid creating another function: arr.forEach(arr.push.only(1));

Even know only will return another function base on the parameter to you pass to it.

Still, I think it would be a great addition to the Function.prototype object.

JS4L

# Andrea Giammarchi (10 years ago)

So this style I favorite since I want to avoid creating another function:

this is like believing that fn.bind() won't create a different object/function ... right?

Or you want to lock that function to receive one forever until you unlock it? That's the only way you could mutate the function behavior without creating a new object/function like bind would do.

And since bind is at least 3X slower than fat arrow, why would you do that?

# Jordan Harband (10 years ago)

arr.push is Array.prototype.push. If you want it bound to arr, you'd need to use .bind or actually call it with arr.push(). arr.push.only would lose the context of the "arr", so that's not an option for your use case as described.

Arrow functions (with Array#map perhaps?) are your best bet here.

# Emanuel Allen (10 years ago)

So this style I favorite since I want to avoid creating another function:

this is like believing that fn.bind() won't create a different object/function ... right?

I like how you pick out my word (like a certain gender group would) even know I re correct my self right after that with:

Even know only will return another function base on the parameter to you pass to it.

Sent from my iPhone

# Emanuel Allen (10 years ago)

Yes I was thinking that too. But if it just default to binding to the object on which the method is being call on it self since this is technically an partial application function.

Or it can have a forth optional parameters to allow what object should be this. Or can simple just use bind call or apply method.

Sent from my iPhone

# Andrea Giammarchi (10 years ago)

(like a certain gender group would)

what is this ?

Anyway, you had your answers, I guess.

Take care

# Michael Haufe (10 years ago)

...but you can do this:

[].push.apply(arr1,arr2);

# Emanuel Allen (10 years ago)

kudos to you sir or ma'am, It work!

var arr = [9,8,7,'a','b','c'], arr2 = [];

[].push.apply(arr2,arr);

arr2;// [9,8,7,'a','b','c']

JS4L

# Dmitry Soshnikov (10 years ago)

In ES2015 (available today via transpilers), one can do:

arr1.push(...arr2);

Dmitry

# Emanuel Allen (10 years ago)

You mean by a library.... I favorite native support over importing a library.:. Although that will change ones import and export are supported. The pain of knowing that it was in Firefox and Netscape at one point in time.

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