JavaScript的基础语法和数据类型详解

<script>
	alert("hello world");
</script>

<script src="js/abc.js"></script>

<script>
    var num = 1;
    alert(num);
</script>

if (2>1)
{
    alert("true");
}

<script>
    var score = 65;
    // alert(num);
    if (score>60&&score<70)
    {
        alert("60-70")
    }
    else if (score>70&&score<80)
    {
        alert(70-80)
    }
    else
    {
        alert("other")
    }
</script>

123  //整数123
123.1   //浮点数123.1
1.122e3   //科学计数法
NaN  //not a number
Infinity  //无限大

'a' "abc"

\'
\n   //换行
\t   //空格
\u4e2d   //unicode编码
\x41    //ascii

var str = `haha
        nihao
        666`

let name='xay';
let words=`你好，${name}`;

word.length

word.toUpperCase()
word.toLowerCase()

substring(1)  //从第一个字符串截取到最后一个
substring(1,3)  //[1,3)

true false

&& //与
|  //或
!  //非

=
==  //类型不一样，值一样也是真
===  //绝对等于，类型和值都必须一样

<script>
    var arr = [1,2,3,4,5,'hello']
</script>

var person = {
    name: 'xay',
    age: 18,
    tags: ['js','java','python']
}

if (2>1)
{
    alert("true");
}

<script>
    var score = 65;
    // alert(num);
    if (score>60&&score<70)
    {
        alert("60-70")
    }
    else if (score>70&&score<80)
    {
        alert(70-80)
    }
    else
    {
        alert("other")
    }
</script>

age=0;
while (age<100)
{
    age+=1;
    console.log(age);
}

for (let i = 0; i < 5; i++) {
    console.log(i);
}

var arr=[1,2,3,4,5,6,7,8,9,10];
for (var num in arr)
{
    console.log(num)
}

var map=new Map([['tom',100],['jack',90],['haha',80]]);
var name=map.get('tom');  //通过key获得value
console.log(name)

map.set('admin',10);
map.delete('tom')  //map中的删除

var set=new Set([3,1,1,1,1]);

set.add(2)  //添加
set.delete(1)  //删除
console.log(set.has(3));  //是否存在3

var map=new Map([['tom',100],['jack',90],['haha',80]]);
for (let x of map)
{
    console.log(x);
}

var set=new Set([3,1,1,1,1]);
for (let x of set)
{
    console.log(x);
}