调用unlockMaterial函数时数组参数materialCosts为何返回undefined？

I'm calling the function unlockMaterial('Ore', 0, ['money', 100]) with the following definition:

function unlockMaterial (material, index, materialCosts) {
    console.log(material)
    console.log(index)
    console.log(materialCosts)
}

But the console outputs Ore 0 undefined. I can't figure out why the materialCosts array is coming through as undefined. For context, I plan to use a similar call pattern later for another function: craftItem(material, array).

Let's break down the possible reasons why your materialCosts parameter is showing up as undefined—your initial function definition and call look syntactically correct, so this is likely a hidden issue in your code:

1. Your function was redefined elsewhere with fewer parameters #

It’s common to accidentally overwrite a function later in your code. If somewhere after the original unlockMaterial definition, you have another version that only accepts 2 parameters, that’s the one being executed:

// This later definition replaces the original
function unlockMaterial(material, index) {
  console.log(material);
  console.log(index);
  console.log(materialCosts); // materialCosts isn't a parameter here, so it's undefined
}

To verify this, log the function’s source code right before your call:

console.log(unlockMaterial.toString());

This will show you the actual function definition that’s being used.

2. A typo or hidden error in your function call #

Double-check the line where you call unlockMaterial:

• Did you accidentally omit the third parameter entirely? (e.g., unlockMaterial('Ore', 0) instead of including the array)
• Is the array being passed as a variable that’s accidentally set to undefined? (e.g., const costs = undefined; unlockMaterial('Ore', 0, costs))
• Did you use invalid syntax for the array? (Like Chinese brackets 【】 instead of square brackets []—though this would throw a syntax error, so your code wouldn’t run at all if this were the case)

3. The parameter is being shadowed inside the function #

If you have a variable named materialCosts defined inside the function, it will overwrite the input parameter:

function unlockMaterial (material, index, materialCosts) {
  let materialCosts = undefined; // This shadows the input parameter
  console.log(material);
  console.log(index);
  console.log(materialCosts); // Logs the internal undefined variable, not the input
}

Scan the function body for any declarations of materialCosts that might be causing this conflict.

For your upcoming craftItem call #

Keep these same checks in mind:

• Confirm the craftItem function accepts the number of parameters you’re passing
• Avoid redefining the function later in your code
• Make sure no internal variables shadow the array parameter

内容的提问来源于stack exchange，提问作者bejewelled