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

Empty null, which is an object type. The object type object has There are many 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 numerical 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 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

2.3 Convert to Boolean()

Tips:

Number conversion Boolean non-zero is true

Convert string to boolean and non-empty is true

NaN null undefined Convert 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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