The index expression is not of type 'number', which is why it is implicitly classified as an 'any' type in this scenario

Utilizing the Zxing Scanner component within Angular version 12 has led me to encounter this particular error on multiple occasions.

/**
 * Returns a valid BarcodeFormat or fails.
 */
private getBarcodeFormat(format: string | BarcodeFormat): BarcodeFormat {
  return typeof format === 'string'
    ? BarcodeFormat[format.trim().toUpperCase()]
    : format;
}

The error resides in this line [format.trim().toUpperCase()] and when I hover over it, the message 

Element implicitly has an 'any' type because index expression is not of type 'number'.ts(7015)
is displayed.

What could be causing this error? How can it be resolved?

I am seeking a solution that does not require any modifications to my angular.json or package.json configurations.

javascriptangulartypescriptzxingangular12

Answer №1

The issue arose due to the fact that format is a variable of type string, which can hold any value. This ambiguity causes TypeScript to be uncertain if format matches one of the keys in BarcodeFormat.

In order to resolve this, we must explicitly inform TypeScript that format belongs to the keys in BarcodeFormat.

To achieve this, we utilize the combination of keyof typeof to retrieve the keys within BarcodeFormat and perform type casting on format.

private getBarcodeFormat(format: string | BarcodeFormat): BarcodeFormat {
    return typeof format === "string"
      ? BarcodeFormat[format.trim().toUpperCase() as keyof typeof BarcodeFormat]
      : format;
}

For a demonstration, you can view the example on codesandbox.

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