null undefined

The undefined type has only one value, which is undefined. When the declared variable is not initialized, the default value of the variable is undefined.The null type also has only one value, which is null. Null is used to represent an empty object

var A1;var a2 = true;var a3 = 1;var a4 = "Hello";var A5 = new Object ();var a6 = null;var a7 = NaN;var a8 = undefined;Alert (typeof a); Show "Undefined"Alert (typeof A1); Show "Undefined"Alert (typeof A2); Show "Boolean"Alert (typeof A3); Show

There are two primitive types in javascript: null and undefined. These two types often make JavaScript developers confused, when is null, and when is undefined?The Undefined type has only one value, which is Undefined. When the declared variable has

Directory1 History 2 clarifying misunderstandings 3 basic concepts 4 features 5 different from Java 6 development toolsHistoryProbably in 1992, a company called Nombas began developing an embedded scripting language called C-minus (C-minus-minus, or

Both shallow and deep copies are only for complex objects such as Object, array,Difference: Shallow copy copies only the first-level properties of objects, deep copies can recursively replicate the properties of an objectIf an array element is a

1. In addition to the addition of string participation, when a value of a non-number type is evaluated, the values are converted to number and then evaluatedvar res = true + +;Console.log (RES); =101var res1 = true + false;Console.log (res1);//=1var

This chapter focuses on data types (basic types and reference types) in JavaScript, variables (including the scope of variables), operators (primarily some of the more common but not easily understood operators). Because of the "all objects" in

Difference between Null and Undefined in JavaScript This article mainly introduces the difference between Null and Undefined in JavaScript. This article provides multiple code instances to explain the differences between them. For more information,

1. The main difference between null and undefined in JScript is that the operation of NULL is like the number 0, while the operation of undefined is like a special value Nan (not a number). The comparison of null values and undefined values is

  Attribute operations mainly introduce the implementation of the three interfaces prop, attr, and val. Compared with other interfaces, these three source code implementations are complex and more confusing, if you accidentally use the wrong

The following sections describe a reasonable modern JavaScript development style guide, not a hard rule. Thelawofcodestyleconsistency is a highly unified code style ). The style you choose for the project should be the highest criterion. Place the

This article begins with the introduction of javascript data types, and then describes the six types of javascript data: Number, Boolean, String, Null, Undefined, and Object, the following is an example of the typeof operator. 1. What is the data

This chapter describes the data types (Basic Types and reference types), variables (including the scope of variables), and operators (mainly common, but not operators that can be understood literally ). Because "Everything is an object" in

This article will focus on the basic concepts in JavaScript. These concepts are quite different from those in traditional languages. Therefore, we will list a separate chapter for specific descriptions to understand the concepts of this chapter and

Chapter III: Basic ConceptsECMAScript There are 5 simple data types (also called basic data types):Undefined\null\boolean\number\string, Another complex data type , --object,object , is essentially composed of a set of unordered name-value pairs.

1. Basic knowledge:Data type:1. Type analysis:There are 8 kinds of data types in JS, the first 5 is the base type and the last 3 are reference types.The difference between Undefined,null,nan in the focus 1:js:：From the above code and running results,

(i) JavaScript type1. JavaScript data types have a total of 6 in the ES5 Standard: Numbers, strings, Booleans, null,undefined, objects. The first five are known as primitive types, and objects are object types. Objects also include our commonly used

ArticleDirectory Object Array Define functions Global Object Insert time of semicolon Reserved Words Reprinted: http://svza.blogspot.com/2007/03/javascript_09.html here format may look good (this seems to have. Flip.

one, Variable 1. Variable name: Variable name starts with $, letter, underscore Hump Naming method Variable names make sense 2. Variable declaration Declaring multiple Variables:var message, name, age; Duplicate

Zendstudio software warning. There is no problem in code running, and there is no problem in writing other software, but there will be a small yellow warning in zend studio. do you know how to block this warning when using this software? Reply