null vs undefined

Accidentally saw a foreigner wrote the discussion JavaScript in undefined and null article, I also learn to translate a back. Find this English is not to rust. Original English:

The difference between null and undefined1. Types of differencesConsole.log (typeof (undefined));//undefinedConsole.log (typeof (null));//objectConsole.log (null==undefined);//trueConsole.log (null===undefined);//false------------extension, why

varVar1;console.log (typeofVAR0);//print "Undefined", the main look under the face of var0 separate outputConsole.log (typeofVAR1);//print "undefined"Console.log (typeof true);//print "Boolean"Console.log (typeof false);//print "Boolean"Console.log (

Demand:A, read a| in turn b| C three files and terminates immediately if there is a failure.B, simultaneous reading a| b| C three files and terminates immediately if there is a failure.First, callback需求A： Let read = function (code) {if (code)

The two are basically the same, and the only difference is initialization:varA = [],//These is the sameb =NewArray (),//A and B is arrays with length 0C= [' foo ', ' Bar '],//These is the sameD =NewArray (' foo ', ' Bar '),//C and D is arrays with 2

PHP is a loosely typed programming language, and it is an indispensable step in a function to examine the "type" of the passed parameter value and whether the value is null or NULL. Type check Starting with PHP5, PHP allows type

Recently looking at some of es2015 's grammar, the most practical thing is to inherit this new feature. For example, the following code:1$(function(){2 class father{3 Constructor (name, age) {4 This. Name =name;5 This.

Property vs. AttributeBefore we begin formally comparing the two jquery methods of Prop () and attr (), it is necessary to understand the meaning of the property and the attribute two words first. In Chinese, they are all the meanings of attributes,

Grunt vs GulpAlthough Gulp has been out for a long time, but has not been used. Thanks to the recent project needs, try it out, here are a few points to talk about the differences between the use of grunt and gulp, focusing on the problems found

Because the laboratory has a virus-containing software, the network management of the laboratory to seal the export, weekend people do not work. It seems that Raspberry Pi is not playing, so yesterday in the dorm to write Windows program, the most