Several 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 should take a look, I hope it can help everyone.

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 method: typeof a;

0.2console.log() is used to print the part you need on the console

Generally, after entering the HTML file page, right-click and select Inspect, the console will appear, select console You can see the content you printed

In addition: alert() is the page pop-up box to display the content

document.write() is the way to output the content on the page

1. Variables: Before talking about basic data types, let’s first understand how to define 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 a number or a decimal

var a = 10;
console.log(typeof a);//number
var b = 10.6;
console.log(typeof b);//number

String type String, use single quotes or double quotes Any character wrapped in quotation marks

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

is not defined undefined, no value is assigned after the variable is defined, this variable is undefined

var g;
console.log(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 (later learning)

var h = "";
console.log(typeof h);//null

And these five are the five basic data types of JS.

2. Type conversion

Mutual conversion between numeric type, string type and Boolean type

2.1 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));//NaN

Note: NaN: not a number, others will be explained later

2.2 Convert to 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

2.3 Convert to Boolean()

Tips:

Convert a number to boolean, non-zero is true

Convert a string to boolean, if it is not empty, it is true

NaN null undefined, convert a string to false

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));//false

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About the difference between basic data types and reference data types in js

Detailed introduction to basic data types in JS development

Introduction to JavaScript basic data types, value types and reference types

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