<! DOCTYPE HTML>
<HTML>
<head>
<Meta charset = " UTF-. 8 " >
<title> </ title>
</ head>
<body>
<Script type = " text / JavaScript " >
// the Math Objects' with class called directly without creating objects
// 1. property
. 1 . .PI // [pi]
2 . .SQRT1_2 // return the reciprocal square root of two (approximately equal to 0.707).
. 3 . .SQRT2 // returns the square root of two (approximately 1.414).
// ...
// 2. The method
// .Round 1. () // rounded to the nearest integer
// 2. .random () // a randomly generated number between (0-1)
// randomly generates an integer between [XY]
// Math.round ( math.random () * (YX) + X);
var a = Math.round (Math.random () * . 5 + 15 ); // randomly generates a number between a 10-15
console.log (a);
// 3. .ceil () // rounded up
the console.log (Math.floor ( 1.6 )); // 2
// 4. .floor () // rounded down
console.log (Math.ceil ( 1.6));//1
// 5. .max(1,2,3,...) //
// ...
// https://www.w3cschool.cn/jsref/jsref-obj-math.html
// 1.String objects
// var STR = new new String ( "W is the Hello")
var STR = " the Hello W is "
// 2. Attribute
1 .str.length
2 .str [ 0 ]
// 3. Method
1 . the charAt ( 0 ) // STR [0]
2 . .toUpperCase () // string to uppercase
. 3 . .toLowerCase () //
. 4 . .indexOf (a, b) // If the write b, from the start b back to find whether a string containing the contents of a location of the first occurrence of the specified
// have to return to its smallest subscript
// No, return -1
5 . .LastIndexOf () // Similar 4, after looking forward to return to a position for the first time, the biggest index
6 . .Split ( "" ) // If write to its going to be split array
...
// https://www.w3cschool.cn/jsref/jsref-lastindexof.html
</script>
</body>
</html>