null or undefined

Personally think that this problem is generally not in accordance with the norms of writing, but lazy people have lazy ways.Page refactoring generally solves this problem, but there is still a workaround for situations where rewriting is

When the project is always using Datagird, the resulting interface, such as a function button on the original title, disappears at this timeError: SCRIPT5007: Could not get the value of the property "RowSpan": the object is null or undefined,The

Echarts cannot get the value of the attribute "getAttribute": the object is null or undefined. Solution: echarts When using Baidu's echarts, when running in IE9, sometimes errors such as the question are reported, and sometimes refreshed and normal.

1. Judge whether each other is equalfunction Btnclick () {alert (null = = NULL);//true alert (undefined==undefined);//true alert (Nan==nan);//false}Summarize:(1) Two null is equal(2) Two undefined are equal(3) Two Nan is unequalfunction Btnclick () {

operator operators, in the front-end interview topics often appear, many friends in their operations often error. Description of the operator operation is not fully understood, I earlier in an article, JavaScript double equals type conversion,

First, let's do some questions first! In order to unify, I do not mix to write these questions, the interview topic, often will these questions mix up, such to your confusion will be bigger, in order to be more convenient demonstration, I here the

Chapter III Basic Concepts Everything in ECMAScript (variables, function names, and operators) is case-sensitive. Identifiers are the names of variables, functions, attributes, or parameters of a function. The constituent rules for

Six Types of javascript data and special notes This article mainly introduces six types of javascript data and special notes. For more information, see Six common data types in js: String, Null, Number, Boolean, and Object.   1. Notes for

There are two special values in JavaScript: undefined and null, which need to be noticed when comparing them. The undefined value is obtained when reading an unassigned variable or attempting to read an attribute that is not in an object.

Six common data types in js: String, Null, Number, Boolean, and Object. 1. Note that the typeof operator involves the data type. Note: 1. typeof is an operator, not a method. Although SyntaxHighligh is often used in js, the following six data types

The six data types that are common in JS are: string, NULL, number, Boolean, type Object.1, typeof Point of attentionWhen it comes to data types, it inevitably mentions that the operator typeof. Be aware that:1, typeof is an operator, not a method.

Six types of data that are common in JS: string type, NULL type, Number type, Boolean type, Object type. 1, typeof Point of attention Involving data types, it is unavoidable to mention that operator TypeOf. To note: 1, typeof is an operator, not

wrote a str = "s" + +;Then nan appeared for a while.The information collected is as follows:1. Judge undefined:The code is as follows:1 style= "Font-size:small;" > var tmp = undefined; 2 if (typeof (tmp) = = "undefined") {3alert ("undefined"); 4

This article mainly introduces how to judge null, undefined, and NaN in JS. If you need it, you can refer to the following str = "s" ++; Then Nan appears. Find it for a while. The collected data is judged as follows: 1. Determine undefined: The

In javascript, how does one determine whether a variable is null, undefined, Or NaN? Let's take a look at the specific judgment method. It is mainly determined through the typeof method. typeof returns a string and has six possible results: "number",

Str = "s" ++;Then Nan appears. Find it for a while.The collected data is judged as follows:1. Determine undefined:Copy codeThe Code is as follows: var tmp = undefined;If (typeof (tmp) = "undefined "){Alert ("undefined ");} Note: typeof returns a

In the JavaScript this keyword detailed article, we talked about the following to make a simple review:The meaning of a 1.this object is to point to properties and methods in the current object.The variability of the 2.this point. This points to the

Source of the 1.call/apply/bind method　　First, when using the Call,apply,bind method, it is necessary to know where these three methods come from. Why is it possible to use these three methods?Call,apply,bind these three methods are actually

Grammar Strict mode enables strict mode to add "use strict" above the top of the script or inside the function; Statement. Data type typeoftypeof returns a undifined,boolean,number,string,object,function of six strings, typeof null

1. Judge undefined:? 1234 vartmp = undefined; if(typeof(tmp) == "undefined"){ alert("undefined"); } Description: typeof returned a string of six possible types: "Number", "string", "Boolean", "Object", "function",