JavaScript Basics (I) Basic types

Small knowledge, big challenge! This article is participating in the creation activity of “Essential Tips for Programmers”.

preface

• Start with javascript basic data types
• Let’s have fun learning!

JavaScript basic data types

• Number Number type
• It is usually an integer

let num = 10 / / decimal
let num = 0xA // hexadecimal 10
let num = 070 // octal 56
typeof num // Number
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• Floating point types

let num = 1.1
let num = 0.1
let num = 1. // Equivalent to 0.1
typeof num //Number
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• Special existence

let num = (0/0) //NaN
typeof NaN // number means that no number is used to indicate that the numeric operation failed
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• String String type
• You can use' 'and""Or ‘ ‘to define strings
• Strings are immutable and cannot be changed once they are created
• You need to destroy it before you create it

let str = 'hello'
let str = "world"
let str = `vike`
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• Boolean Indicates the Boolean type
• There are two Booleanstrue 和false

• Undefined has only one value and is Undefined
• Use var or let to declare variables undefined if they have no value assigned

// The variable is promoted
console.log(a)  //undefined
var a

// let has no variable promotion
let b
console.log(b) //undefined
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• Null has only one value that is null
• Null represents a null pointer object

typeof null //object

// undefined is derived from null
undefined= =null //true
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• Instances of symbols are unique and immutable

let symbol1 = Symbol(a)let symbol2 = Symbol(a)console.log(symbol1 == symbol2)  // false
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• BigInt Specifies a value outside the Number range

// The unit of BigInt is n
let num = 2n
typeof num // 'bigint'
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JavaScript reference type

• Object Object type
• Creating an object usually uses the object literal notation

let obj = {
    a:1.'a':1.3:2
}
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• Array Array type
• An ordered set of data

let arr = [1.2.3]
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• Function Type

// Function declaration
function fn() {}

// Function expression
let fn = function() {}

// Arrow function
let fn = x= > x
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conclusion

• I like to get a thumbs up