How to Use fs. truncate in node. js _ node. js-js tutorial

This article mainly introduces node. fs. the truncate method is described in this article. methods, syntax, parameters, instances, and source code for truncate. For more information, see Method description:

File Content truncation.

Syntax:

The Code is as follows:

Fs. truncate (path, len, [callback (err)])

Because this method belongs to the fs module, we need to introduce the fs module (var fs = require ("fs") before use "))

Receiving parameters:

Path file path

Len truncation length. Only characters within the length of this character are retained. The excess part is cleared.

Callback, passing an exception parameter err

Example:

The Code is as follows:

Var fs = require ('fs ');
Fs.truncate('126.txt ', 2, function (err ){
If (err ){
Throw err;
}
Console. log ('file content truncated successfully ');
})

Source code:

The Code is as follows:

Fs. truncate = function (path, len, callback ){
If (util. isNumber (path )){
// Legacy
Return fs. ftruncate (path, len, callback );
}
If (util. isFunction (len )){
Callback = len;
Len = 0;
} Else if (util. isUndefined (len )){
Len = 0;
}
Callback = maybeCallback (callback );
Fs. open (path, 'r + ', function (er, fd ){
If (er) return callback (er );
Binding. ftruncate (fd, len, function (er ){
Fs. close (fd, function (er2 ){
Callback (er | er2 );
});
});
});
};