Float numbers not pushed into array.

In two words: float numbers not pushed into array if in push function shift is called.

Version: 8.5.0
Platform: linux x86_64

class FixedArray extends Array {
  constructor(length) {
    super(length);
    this.maxLength = length;
  }

  push(...args) {
    console.log('what to push', args);
    super.push.apply(this, args);
    console.log('array after push', this);
    if (this.length > this.maxLength) {
      console.log('what is shifted?', super.shift.apply(this));
    }
  }
}

var ddd = new FixedArray(30);
ddd.push(1);
ddd.push(2);
ddd.push(3);
ddd.push(0.4);
ddd.push(0.5);
ddd.push(0.6);
console.log(ddd);

Result:

what to push [ 1 ]
array after push FixedArray [ <30 empty items>, 1, maxLength: 30 ]
what is shifted? undefined
what to push [ 2 ]
array after push FixedArray [ <29 empty items>, 1, 2, maxLength: 30 ]
what is shifted? undefined
what to push [ 3 ]
array after push FixedArray [ <28 empty items>, 1, 2, 3, maxLength: 30 ]
what is shifted? undefined
what to push [ 0.4 ]
array after push FixedArray [ <27 empty items>, 1, 2, 3, 0.4, maxLength: 30 ]
what is shifted? undefined
what to push [ 0.5 ]
array after push FixedArray [ <27 empty items>, 1, 2, 3, 0.5, maxLength: 30 ]
what is shifted? undefined
what to push [ 0.6 ]
array after push FixedArray [ <27 empty items>, 1, 2, 3, 0.6, maxLength: 30 ]
what is shifted? undefined
FixedArray [ <27 empty items>, 1, 2, 3, maxLength: 30 ]

Here's the code that stopped working in 8.5.0, but it was working in 8.4.0.

There's a class FixedArray that basically overrides push method. When I try to push float value into such array it pushes only once, however it should be pushed every second.

Another strange thing is if you change it to ddd.push(5); it works normally and integer value is pushed into this array every second.

If you remove shift() from a push, then all works also normally.

PS: In chrome versions from 60 to 63 all works normally.

Simplified case:

'use strict';

var ar = new Array(5);

ar.push(1);
console.log(ar);

ar.shift();
console.log(ar);

ar.push(2);
console.log(ar);

ar.shift();
console.log(ar);

ar.push(0.3);
console.log(ar);

ar.shift();
console.log(ar);

[ <5 empty items>, 1 ]
[ <4 empty items>, 1 ]
[ <4 empty items>, 1, 2 ]
[ <3 empty items>, 1, 2 ]
[ <3 empty items>, 1, 2, 0.3 ]
[ <3 empty items>, 1, 2 ]

This is fixed in V8 6.1.

/cc @nodejs/v8

@targos

@targos then this is related to #15393

Even more simplified case:

var ar = [, , 0.1];

ar.shift();
console.log(ar);

[ <2 empty items> ]

So the issue is: Array.prototype.shift() skips empty slots till the first float number and shifts this number instead?

@vsemozhetbyt

@vsemozhetbyt I don't think so, because is you look into my example there were some integers before floats and they were not shifted. Also:

var a = [,,,0.4,1,2,3,0.5];
a.shift()
console.log(a) // it will remove 0.5, not 0.4

Yes, it seems for arrays with an initial hole and a non-SMI number, Array.prototype.shift() becomes Array.prototype.pop().

const a = [ , 2**31, 1 ];
a.shift();
console.log(a); // [ <1 empty item>, 2147483648 ]

The commit message here looks like it could be fixing this: v8/v8@81778aa

a variant of Array.prototype.pop(), it pops but doesn't return the value (returns undefined)

v8/v8@81778aa was actually merged to V8 6.1 so this issue is fixed on master.

v8.7.0 was released with V8 6.1, which has the fix. I'll close this out.

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Float numbers not pushed into array. #15427

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Float numbers not pushed into array. #15427

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vsemozhetbyt commented on Sep 15, 2017

targos commented on Sep 15, 2017

targos commented on Sep 15, 2017

SkeLLLa commented on Sep 15, 2017

vsemozhetbyt commented on Sep 15, 2017

SkeLLLa commented on Sep 15, 2017

vsemozhetbyt commented on Sep 15, 2017

targos commented on Sep 15, 2017

andrasq commented on Sep 15, 2017

targos commented on Sep 18, 2017

bnoordhuis commented on Oct 15, 2017

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