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Avoid boolean parameters

Written byPhuoc Nguyen
13 May, 2021
Let's consider a situation where we have a function that writes a string to a file. It allows user to append the content to file, or override the content via the `override` parameter:
const writeToFile = (content: string, file: string, override: boolean) => {
With that signature, the function will be invoked as following
// Append the content to file
writeToFile(content, file, true);

// Override the file
writeToFile(content, file, false);
If you are not the one who creates the function, you have to question what the boolean value represents until looking at the implementation.
It is worse if the function has a lot of boolean flags. Using boolean flags makes the core harder to read and maintain.
There are a few ways to get rid of the issue.

Provide explicit methods

appendToFile(content, file);
overrideFile(content, file);

Use an object parameter

writeToFile(content, file, { override });

Use an enum

If you're using TypeScript, then you can use `enum` to represent the possible values of a boolean flag.
enum SaveMode {

writeToFile(content, file, mode: SaveMode);
It's confident for consumers to call the method:
writeToFile(content, file, SaveMode.Append);

// Or
writeToFile(content, file, SaveMode.Override);

See also

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Phước Nguyễn