An issue in JerryscriptProject jerryscript v.3.0.0 allows an attacker to obtain sensitive information via a crafted script to the arrays.
# Version

*Version: 3.0.0* ( 6fe763f )

# Execution steps

```bash
/root/.jsvu/jerry Testcase.js
```

# Test case 1

```javascript
var foo = function(it) {
    var a = [...it, , ];
    print(a);
    print(a.length);
};
var Parameter0 = [1, 2];
foo(Parameter0);
```

## Output 1

```
1,2
2
```

## Expected behavior

```
1,2,
3
```

# Test case 2

```javascript
var foo = function(it) {
    var arr = [ , ];
    var a = it.concat(arr);
    print(a);
    print(a.length);
};
var Parameter0 = [1, 2];
foo(Parameter0);
```

## Output 2

```
1,2,
3
```

# Description

We tested on multiple JS engines, Testcase 1 and Testcase 2 should have the same consequent. But jerryscript outputs abnormal results when executing Testcase 1.

Maybe the problem is about array literal handling which looks like it deleted all the vacancies. The same bug has reported to Hermes(https://github.com/facebook/hermes/issues/729) and has been fixed. 

Looking forward to your reply :)
Array concatenation exception
This is a GitHub Issue
repo:jerryscript
owner:jerryscript-project
Title : Array concatenation exception
Issue date:

--- start body ---
# Version

*Version: 3.0.0* ( 6fe763f )

# Execution steps

```bash
/root/.jsvu/jerry Testcase.js
```

# Test case 1

```javascript
var foo = function(it) {
    var a = [...it, , ];
    print(a);
    print(a.length);
};
var Parameter0 = [1, 2];
foo(Parameter0);
```

## Output 1

```
1,2
2
```

## Expected behavior

```
1,2,
3
```

# Test case 2

```javascript
var foo = function(it) {
    var arr = [ , ];
    var a = it.concat(arr);
    print(a);
    print(a.length);
};
var Parameter0 = [1, 2];
foo(Parameter0);
```

## Output 2

```
1,2,
3
```

# Description

We tested on multiple JS engines, Testcase 1 and Testcase 2 should have the same consequent. But jerryscript outputs abnormal results when executing Testcase 1.

Maybe the problem is about array literal handling which looks like it deleted all the vacancies. The same bug has reported to Hermes(https://github.com/facebook/hermes/issues/729) and has been fixed. 

Looking forward to your reply :)
--- end body ---

The issue describes a discrepancy in array handling between JerryScript and other JavaScript engines, specifically regarding the treatment of empty slots in arrays. However, this does not indicate a security vulnerability, but rather a bug in the implementation of array concatenation and handling of empty slots.