Jsgen: Index Is Not Defined In Array Initialization

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Describe the bug

The bug occurs when trying to initialize an array in V programming language using the index variable. The error message indicates that index is not defined, which prevents the compilation of the code.

Reproduction Steps

To reproduce the bug, follow these steps:

  1. Create a new file named main.v with the following content:
fn main() {
	// items := []string{len: 3, init: 'Item ${it}'} // OK!
	items := []string{len: 3, init: 'Item ${index}'} // Nope!
	println(items)
}
  1. Save the file and navigate to the terminal.
  2. Compile the V code to JavaScript using the following command:
v -b js main.v
  1. Execute the generated JavaScript code using Node.js:
node main.js
  1. Observe the error message, which should indicate that index is not defined.

Expected Behavior

The expected behavior is that the code should compile successfully and print the initialized array to the console.

Current Behavior

The current behavior is that the code does not compile due to the undefined index variable.

Possible Solution

One possible solution is to use the it variable instead of index when initializing the array. This is because it is a valid variable in V programming language that can be used to access the current index of the array.

Additional Information/Context

No additional information or context is provided.

V version

The V version used to reproduce the bug is 0.4.10 (0cb1366).

Environment details (OS name and version, etc.)

The environment details are as follows:

V full version V 0.4.10 dead5e69b44b4f8c4999ac82b730c21250cb0583.0cb1366
OS macOS, macOS, 15.4.1, 24E263
Processor 8 cpus, 64bit, little endian, Apple M1 Pro
Memory 0.5GB/16GB
V executable /Users/gonzalo/Projects/Personal/v/nv/v
V last modified time 2025-05-03 07:31:04
V home dir OK, value: /Users/gonzalo/Projects/Personal/v/nv
VMODULES OK, value: /Users/gonzalo/.vmodules
VTMP OK, value: /tmp/v_501
Current working dir OK, value: /Users/gonzalo/Projects/Personal/v/myapp
Git version git version 2.39.1
V git status weekly.2025.18-6-g0cb1366c
.git/config present true
cc version Apple clang version 17.0.0 (clang-1700.0.13.3)
gcc version Apple clang version 17.0.0 (clang-1700.0.13.3)
clang version Apple clang version 17..0 (clang-1700.0.13.3)
tcc version tcc version 0.9.28rc 2024-02-05 HEAD@105d70f7 (AArch64 Darwin)
tcc git status thirdparty-macos-arm64 e447816c
emcc version N/A
glibc version N/A

Conclusion

The bug occurs due to the undefined index variable when initializing an array in V programming language. The possible solution is to use the it variable instead of index. This bug can be reproduced using V version 0.4.10 on macOS with the specified environment details.

Solution

To fix the bug, replace the index variable with it in the array initialization:

fn main() {
	items := []string{len: 3, init: 'Item ${it}'} // OK!
	println(items)
}

This should compile the code successfully and print the initialized array to the console.

Example Use Case

Here's an example use case that demonstrates the fixed code:

fn main() {
	items := []string{len: 3, init: 'Item ${it}'} // OK!
	println(items)
}

Output:

[Item 0, Item 1, Item 2]

This example shows that the fixed code initializes an array with three elements and prints the array to the console.

Q: What is the issue with using index to initialize arrays in V programming language?

A: The issue is that index is not defined in the context of array initialization, resulting in a compilation error.

Q: What is the expected behavior when initializing arrays in V programming language?

A: The expected behavior is that the code should compile successfully and initialize the array with the specified elements.

Q: What is the current behavior when initializing arrays in V programming language?

A: The current behavior is that the code does not compile due to the undefined index variable.

Q: What is the possible solution to fix the bug?

A: The possible solution is to use the it variable instead of index when initializing the array.

Q: Why is it a valid variable in V programming language?

A: it is a valid variable in V programming language because it is used to access the current index of the array.

Q: Can you provide an example of the fixed code?

A: Yes, here's an example of the fixed code:

fn main() {
	items := []string{len: 3, init: 'Item ${it}'} // OK!
	println(items)
}

Q: What is the output of the fixed code?

A: The output of the fixed code is:

[Item 0, Item 1, Item 2]

Q: Can you provide more information about the environment details used to reproduce the bug?

A: Yes, here are the environment details used to reproduce the bug:

V full version V 0.4.10 dead5e69b44b4f8c4999ac82b730c21250cb0583.0cb1366
OS macOS, macOS, 15.4.1, 24E263
Processor 8 cpus, 64bit, little endian, Apple M1 Pro
Memory 0.5GB/16GB
V executable /Users/gonzalo/Projects/Personal/v/nv/v
V last modified time 2025-05-03 07:31:04
V home dir OK, value: /Users/gonzalo/Projects/Personal/v/nv
VMODULES OK, value: /Users/gonzalo/.vmodules
VTMP OK, value: /tmp/v_501
Current working dir OK, value: /Users/gonzalo/Projects/Personal/v/myapp
Git version git version 2.39.1
V git status weekly.2025.18-6-g0cb1366c
.git/config present true
cc version Apple clang version 17.0.0 (clang-1700.0.13.3)
gcc version Apple clang version 17.0.0 (clang-1700.0.13.3)
clang version Apple clang version 17..0 (clang-1700.0.13.3)
tcc version tcc version 0.9.28rc 2024--05 HEAD@105d70f7 (AArch64 Darwin)
tcc git status thirdparty-macos-arm64 e447816c
emcc version N/A
glibc version N/A

Q: Can you provide more information about the V programming language?

A: Yes, here's more information about the V programming language:

  • V is a statically typed, compiled language that is designed to be fast and efficient.
  • V is a general-purpose language that can be used for a wide range of applications, including systems programming, embedded systems, and high-performance computing.
  • V is designed to be easy to learn and use, with a simple and intuitive syntax.
  • V is a compiled language, which means that the code is compiled into machine code before it is executed.
  • V is a statically typed language, which means that the type of each variable is known at compile time.

Q: Can you provide more information about the it variable in V programming language?

A: Yes, here's more information about the it variable in V programming language:

  • it is a built-in variable in V programming language that is used to access the current index of an array.
  • it is a read-only variable, which means that it cannot be assigned a new value.
  • it is a numeric variable, which means that it can only hold integer values.
  • it is a local variable, which means that it is only accessible within the current scope.

Q: Can you provide more information about the index variable in V programming language?

A: Yes, here's more information about the index variable in V programming language:

  • index is a built-in variable in V programming language that is used to access the current index of an array.
  • index is a read-only variable, which means that it cannot be assigned a new value.
  • index is a numeric variable, which means that it can only hold integer values.
  • index is a local variable, which means that it is only accessible within the current scope.

Q: Can you provide more information about the len variable in V programming language?

A: Yes, here's more information about the len variable in V programming language:

  • len is a built-in variable in V programming language that is used to access the length of an array.
  • len is a read-only variable, which means that it cannot be assigned a new value.
  • len is a numeric variable, which means that it can only hold integer values.
  • len is a local variable, which means that it is only accessible within the current scope.

Q: Can you provide more information about the init variable in V programming language?

A: Yes, here's more information about the init variable in V programming language:

  • init is a built-in variable in V programming language that is used to access the initial value of an array.
  • init is a read-only variable, which means that it cannot be assigned a new value.
  • init is a string variable, which means that it can hold string values.
  • init is a local variable, which means that it is only accessible within the current scope.