JavaScript初级课程 variables

下载node。

1. 申明变量

variables.js

let message = "Hello!";
message = "World";
console.log(message);

node variables.js

2. 申明不会变的变量

const COLOR_GREEN = "green";
console.log(COLOR_GREEN)

3. 数据类型

Data Types = [number, BigInt, string, boolean, null, undefined, Symbol, Object]

// string
let favoriteFruit = 'strawberries';
let favoriteIceCream = "chocolate";
let favoriteProgrammingLanguage = `Javascript`;

// number
let numberOfDonuts = 12;
let pi = 3.14;

// BigInt
let veryLargeNumber = 5435434363466n;

// boolean
let lovesCoding = true;

// undefined
let favoriteColor;
console.log(favoriteColor);

// null
favoriteFruit = null;

// Symbol
const uniqueKey = Symbol();

// Object
let course = {
    name: 'JavaScript',
    hours: 3
}

4. 动态类型

let firstName = 'Steven';
console.log(typeof firstName);

firstName = 100;
console.log(typeof firstName);

firstName = true;
console.log(typeof firstName);

string
number
boolean

5. Objects

let course = {
    name: 'JavaScript',
    hours: 3
};

console.log(course.name);

course.name = 'Python';
console.log(course.name);

console.log(course['name']);

course['name'] = 'Java';
console.log(course['name']);

let property = 'hours';
console.log(course[property])

JavaScript
Python
Python
Java
3

6. Arrays

let productColors = ['blue', 'green'];

console.log(productColors[0])

productColors[0] = 42;

console.log(productColors[0])
console.log(productColors.length)

blue
42
2

7. Functions

function sayHi(name){
    console.log('Hi! ' + name);
}

sayHi('Steven');

function multiply(num1, num2) {
    return num1 * num2;
};

console.log( multiply(2, 2) );