What are the basic data types in JS development? JS data types include basic data types, complex data types and special data types. Today we will mainly explain basic data types.
0. First, please remind two of the following knowledge points:
0.1typeof is used to detect variable types
Writing: typeof a;
0.() is used to print the parts you need in the console
Generally, after entering the HTML file page, right-click to select Check, the console will appear. Select console to see what you have printed.
In addition: alert() is the page pop-up box to display content
() is the way to output content in the page
1. Variables: Before talking about basic data types, let’s first understand the method of defining variables in JS.
1.1 Defining variables: When defining a variable, you can give the initial value of the variable without distinguishing between types (types of containers).
1.2 Naming specifications for variables: combinations of letters, numbers, underscores and $; cannot start with numbers; cannot be keywords and reserved words; camel nomenclature.
1.3 The initial value can only be the following 5 types:
Number type, number can only be a number or a decimal
var a = 10; (typeof a);//number var b = 10.6; (typeof b);//number
String type String, any character wrapped in single or double quotes
var c = 'hello'; (typeof c);//string var d = "world"; (typeof d);//string
Boolean type Boolean can only be true or false to represent true or false
var e = true; (typeof e);//boolean var f = false; (typeof f);//boolean
Undefined, no value is assigned after defining the variable. This variable is undefined
var g; (typeof g);//undefined
Empty null is an object type. There are many types of object types, such as array objects, mathematical objects, and date objects (latest learning)
var h = ""; (typeof h);//null
And these five are the five basic data types of JS.
2. Type conversion
Conversion of numeric types, string types and boolean types
2.1 Turn value—Number()
(Number("123"));//123
(Number("12.3"));//12.3
(Number("12hshs"));//NaN
(Number('0034'));//34
(Number(""));//0
(Number(true));//1
(Number(false));//0
(Number(null));//0
(Number(undefined));//NaN
Note: NaN: not a number, others will be explained later
2.2 Turn the string String(), what to write to what to turn
(String(123));//123 (String(0));//0 (String(true));//true (String(false));//false (String(undefined));//undefined (String(null));//null
2.3 to Boolean()
Skill:
Number to boolean is not 0 to true
String to boolean is not empty to true
NaN null undefined to convert string to false
(Boolean("123"));//true
(Boolean("0"));//true
(Boolean("Shandong"));//true
(Boolean(""));//false
(Boolean("true"));//true
(Boolean("false"));//true
(Boolean(14));//true
(Boolean(0));//false
(Boolean(NaN));//false
(Boolean(-100));//true
(Boolean(undefined));//false
(Boolean(null));//false
Summarize
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