ES6-ES13学习笔记（4.0）

news2025/1/11 0:17:36

includes函数判断字符串是否存在指定字符

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    <title>Document</title>
</head>
<body>
    <script>
        let myname="kunkun"
        console.log(myname.includes("ku"))
        console.log(myname.includes("a"))
        console.log(myname.includes("u",2))//传第二个参数，以指定索引开头进行查找
        console.log(myname.startsWith("k"))
        console.log(myname.endsWith("n"))//end的第二个参数是从后往前的索引

        console.log(myname.repeat(2))

        console.log(myname.repeat(2.3))
        console.log(myname.repeat(0))
        
    </script>
</body>
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startsWith函数判断自发货窜是否以指定的字符串开头

endsWith函数判断字符串是否以指定的字符串结尾

repeat函数重复字符串（默认是重复一次。如果传入的参数为0，那么就会输出空字符串）

ES6支持了二进制，八进制的转换

2. Number.isFinite Number.isNaN

它与传统的全局方法isFinite()和isNaN()的区别在于，传统方法先调用Number()将非数值的值转为数值，再进行判断，而这两个新方法支队数值有效，Number.isFinite()对于非数值一律返回false，Number.isNaN()只对NaN返回true，非NaN一律返回false

Number.isInteger 判断是否为整数

3.极小常量 Number.EPSILON

4.取整(舍弃小数部分) Math.trunc

5.Math.sign判断一个数是正数、负数、还是零。对于非数值，会首先转换为数值

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 * @Date: 2023-06-01 08:59:17
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<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        //1 二进制，八进制写法
        let num1=100
        let num2=0x12
        let num3=0b0101
        let num4=0o1210
        console.log(num1)
        console.log(num2)
        console.log(num3)
        console.log(num4)

        //2. Number.isFinite Number.isNaN
        let num5=Number.isFinite(100)//true
        let num6=Number.isFinite(100/0)//false
        let num7=Number.isFinite(Infinity)//false
        let num8=Number.isFinite("1")//false
        console.log(num8)
        let num9=Number.isNaN(100)
        let num10=Number.isNaN(NaN)
        let num11=Number.isNaN("Infinity")
        let num13=Number.isNaN("mez")
        let num12=Number.isNaN("100")
        console.log(num9)
        console.log(num10)
        console.log(num11)
        console.log(num12)
        console.log(num13)
        let num14=Number.isInteger(100)
        let num15=Number.isInteger(100.00)
        let num16=Number.isInteger("Infinity")
        let num17=Number.isInteger("mez")
        let num18=Number.isInteger("100")
        console.log(num14)
        console.log(num15)
        console.log(num16)
        console.log(num17)
        console.log(num18)

        //3.极小常量
        function isEqual(x,y){
            return Math.abs(x-y)<Number.EPSILON
        }
        console.log(isEqual(5,6))
        console.log(isEqual(0.1+0.2,0.3))
        console.log(Number.EPSILON)

        //4.取整(舍弃小数部分)
        console.log(Math.trunc(1.8))
        console.log(Math.trunc(1.1))
        console.log(Math.trunc(-1.8))
        console.log(Math.trunc(-1.1))

        //Math.sign判断一个数是正数、负数、还是零。对于非数值，会首先转换为数值
        console.log(Math.sign(-100))
        console.log(Math.sign(100))
        console.log(Math.sign("-100"))
        console.log(Math.sign(0))
        console.log(Math.sign("mez"))
    </script>
</body>
</html>