In Node.js documentation, API's are listed like a format I am not understanding.

For Example:

1. fs.writeFile(file, data[, options], callback)
2. fs.writeSync(fd, buffer[, offset[, length[, position]]])

I can understand the arguments file and callback but what does it means by data[, options], I want to know the details meaning by data[, options] or buffer[, offset[, length[, position]]]) or like this format.

CodePudding user response：

When you see this:

fs.writeFile(file, data[, options], callback)

It means you can use it in either of these ways:

fs.writefile(file, data, options, callback)
fs.writefile(file, data, callback);

In other words, the options parameter is optional. You can pass it if needed or leave it out if not needed. The fs.writeFile() code will look at the type and quantify of the arguments you passed and determine which of these forms you are using and adapt as necessary.

When you see this:

fs.writeSync(fd, buffer, offset[, length[, position]])

It means that you can use any of these forms:

fs.writeSync(fd, buffer, offset)
fs.writeSync(fd, buffer, offset, length)
fs.writeSync(fd, buffer, offset, length, position)

You cannot use something like:

fs.writeSync(fd, buffer, position) 

because the code would have no way of knowing that the third argument was supposed to be position instead of offset as both are just numeric values. So, if you want to use the position argument, you have to pass all five arguments or use one of the other forms below.

Note that for fs.writeSync(), there are several additional forms that are allowed in nodejs v18. It offers:

fs.writeSync(fd, buffer, offset[, length[, position]])
fs.writeSync(fd, buffer[, options])
fs.writeSync(fd, string[, position[, encoding]])

The second option there is the most flexible as you can fill in the options argument with whichever arguments you want to pass and the others will assume default values.