Instructions for using the fs.truncate method in node.js_node.js

Method description:

File content interception operation.

Grammar:

Copy code The code is as follows:

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

Since this method belongs to the fs module, the fs module needs to be introduced before use (var fs= require(“fs”) )

Receive parameters:

path File path

len truncates the length, retaining only the characters within the character length, and the excess will be cleared.

callback Callback, passing an exception parameter err

Example:

Copy code 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:

Copy 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);
});
});
});
};