util提供了各种使用的工具。require(‘util‘) to access them.

Util.format(format,[..])

Returns a formatted string using the first argument as a printf-like format.

The first argument is a string that contains zero or more placeholders. Each placeholder is replaced with the converted value from its corresponding argument. Supported placeholders are:

• %s - String.
• %d - Number (both integer and float).
• %j - JSON.
• % - single percent sign (‘%‘). This does not consume an argument.

If the placeholder does not have a corresponding argument, the placeholder is not replaced.

util.format(‘%s:%s‘, ‘foo‘); // ‘foo:%s‘

If there are more arguments than placeholders, the extra arguments are converted to strings withutil.inspect() and these strings are concatenated, delimited by a space.

util.format(‘%s:%s‘, ‘foo‘, ‘bar‘, ‘baz‘); // ‘foo:bar baz‘

If the first argument is not a format string then util.format() returns a string that is the concatenation of all its arguments separated by spaces. Each argument is converted to a string with util.inspect().

util.format(1, 2, 3); // ‘1 2 3‘

util.log(string) 

带有时间戳的标准输出。

require(‘util‘).log(‘Timestamped message.‘);输出如下：7 Dec 00:24:04 - ss

util.inspect(object, [options])#

Return a string representation of object, which is useful for debugging.

An optional options object may be passed that alters certain aspects of the formatted string:

• showHidden - if true then the object‘s non-enumerable properties will be shown too. Defaults to false.为true时对象的非枚举类型属性将显示

• depth - tells inspect how many times to recurse while formatting the object. This is useful for inspecting large complicated objects. Defaults to 2. To make it recurse indefinitely pass null.

• colors - if true, then the output will be styled with ANSI color codes. Defaults to false. Colors are customizable, see below.

• customInspect - if false, then custom inspect() functions defined on the objects being inspected won‘t be called. Defaults to true.

Example of inspecting all properties of the util object:

var util = require(‘util‘);console.log(util.inspect(util, { showHidden: true, depth: null }));

Customizing util.inspect colors#

Color output (if enabled) of util.inspect is customizable globally via util.inspect.styles andutil.inspect.colors objects.

util.inspect.styles is a map assigning each style a color from util.inspect.colors. Highlighted styles and their default values are: number (yellow) boolean (yellow) string (green) date (magenta) regexp(red) null (bold) undefined (grey) special - only function at this time (cyan) * name (intentionally no styling)

Predefined color codes are: white, grey, black, blue, cyan, green, magenta, red and yellow. There are also bold, italic, underline and inverse codes.

Objects also may define their own inspect(depth) function which util.inspect() will invoke and use the result of when inspecting the object:

var util = require(‘util‘);var obj = { name: ‘nate‘ };obj.inspect = function(depth) {  return ‘{‘ + this.name + ‘}‘;};util.inspect(obj);  // "{nate}"

util.isArray(object)#

Returns true if the given "object" is an Array. false otherwise.

var util = require(‘util‘);util.isArray([])  // trueutil.isArray(new Array)  // trueutil.isArray({})  // false

util.isRegExp(object)#

Returns true if the given "object" is a RegExp. false otherwise.

var util = require(‘util‘);util.isRegExp(/some regexp/)  // trueutil.isRegExp(new RegExp(‘another regexp‘))  // trueutil.isRegExp({})  // false

util.isDate(object)#

Returns true if the given "object" is a Date. false otherwise.

var util = require(‘util‘);util.isDate(new Date())  // trueutil.isDate(Date())  // false (without ‘new‘ returns a String)util.isDate({})  // false

下面这个很实用：

util.inherits(constructor, superConstructor)#

Inherit the prototype methods from one constructor into another. The prototype of constructor will be set to a new object created from superConstructor.

As an additional convenience, superConstructor will be accessible through the constructor.super_property.

var util = require("util");var events = require("events");function MyStream() {    events.EventEmitter.call(this);}util.inherits(MyStream, events.EventEmitter);MyStream.prototype.write = function(data) {    this.emit("data", data);}var stream = new MyStream();console.log(stream instanceof events.EventEmitter); // trueconsole.log(MyStream.super_ === events.EventEmitter); // truestream.on("data", function(data) {    console.log(‘Received data: "‘ + data + ‘"‘);})stream.write("It works!"); // Received data: "It works!"

node.js模块之util模块