A detailed introduction to basic data types in JS development
The data types of JS include basic data types, complex data types and special data types. Today we will mainly explain the basic data types first. Friends who are interested, let’s take a look
What are the basic data types in JS development? The data types of JS include basic data types, complex data types and special data types. Today we will mainly explain the basic data types first.
0. Let me first remind you of the following two knowledge points:
0.1typeof is used to detect variable types
Writing: typeof a;
0.2console.log() is used to print the part you need on the console
Generally, after entering the HTML file page, click Right-click and select Inspect, and a console will appear. Select console to see what you printed.
In addition: alert() is the page pop-up box display content
document.write() It is the way to output content on the page
1. Variables: Before talking about basic data types, let’s first understand the method of defining variables in JS.
1.1 Define variables: When defining a variable, you can give the variable an initial value, regardless of type (type of container).
1.2 Naming specifications for variables: a combination of letters, numbers, underscores and $; cannot start with a number; cannot be keywords or reserved words; camel case naming method.
1.3 The initial value can only be the following five types:
Numeric type Number, which can only be numbers or decimals
var a = 10; console.log(typeof a);//number var b = 10.6; console.log(typeof b);//number
characters String type, any character wrapped in single quotes or double quotes
var c = 'hello'; console.log(typeof c);//string var d = "world"; console.log(typeof d);//string
Boolean type Boolean, can only be true or false to represent true or false
var e = true; console.log(typeof e);//boolean var f = false; console.log(typeof f);//boolean
Undefined, no value is assigned after defining a variable, this variable is undefined
##
var g; console.log(typeof g);//undefined
var h = ""; console.log(typeof h);//null
2. Type conversion
Mutual conversion between numerical type, string type and Boolean type2.1 Convert value—Number()
console.log(Number("123"));//123
console.log(Number("12.3"));//12.3
console.log(Number("12hshs"));//NaN
console.log(Number('0034'));//34
console.log(Number(""));//0
console.log(Number(true));//1
console.log(Number(false));//0
console.log(Number(null));//0
console.log(Number(undefined));//NaN2.2 Converting characters String(), convert whatever you write
console.log(String(123));//123 console.log(String(0));//0 console.log(String(true));//true console.log(String(false));//false console.log(String(undefined));//undefined console.log(String(null));//null
console.log(Boolean("123"));//true
console.log(Boolean("0"));//true
console.log(Boolean("山东"));//true
console.log(Boolean(""));//false
console.log(Boolean("true"));//true
console.log(Boolean("false"));//true
console.log(Boolean(14));//true
console.log(Boolean(0));//false
console.log(Boolean(NaN));//false
console.log(Boolean(-100));//true
console.log(Boolean(undefined));//false
console.log(Boolean(null));//falseSummarize
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