Detailed explanation of JavaScript's built-in objects Math and strings

Math Objects

• Math is a tool class object that encapsulates properties and methods related to mathematical operations.

Common properties

• Math.PI: represents pi

Common methods

• Math.abs(x) : Returns the absolute value of x
• Math.pow(x,y) : Returns x raised to the power of y
• Math.sqrt(x) : Returns the square root of x
• Math.round(x) : Returns x rounded to the nearest integer
• Math.floor(x) : Returns the largest integer less than or equal to x
• Math.ceil(x) : This function returns the smallest integer greater than or equal to x.
• Math.max() : Returns the maximum value among the arguments
• Math.min() : Returns the minimum value among its arguments

Math.random()

• Returns a pseudo-random number (between 0.0 and 1.0) (excluding 1)
• Generate a random number in [0,x]
  • Math.round(Math.random()*x)
  • [0,10]: Math.round(Math.random()*10)
• Generate a random number [x,y]
  • Math.round(Math.random()*(yx)+x
  • Random number from [1,10]: Math.round(Math.random()*9)+1

String Methods

The length property

• Can be used to get the length of a string

var str = "Hello World!!!";
var result = str.length;
console.log(result);

charAt()

• Can return the character at a specified position in a string
• Get the specified character by index

var str = "Hello World!!!";
var result = str.charAt(6);
console.log(result);

charCodeAt()

• Get the character encoding (Unicode encoding) of the character at the specified position

var str = "Hello World!!!";
var result = str.charCodeAt(6);
console.log(result);

fromCharCode()

• You can get characters according to character encoding

var result = String.fromCharCode(18888);
console.log(result);

concat()

• Can be used to concatenate two or more strings
• Will not affect the original string

var str = "Hello World!!!";
var result = str.concat("Hello","World");
console.log(result);

indexOf()

• This method can retrieve whether a string contains the specified content.
• If the string contains the content, the index of its first occurrence is returned.
• If the specified content is not found, it returns -1
• You can specify a second parameter to specify the position to start searching.

var str = "Hello World!!!";
var result0 = str.indexOf('l');
var result1 = str.indexOf('l',3);//Start from the third position var result2 = str.indexOf('l',5);//Start from the fifth position console.log(result0);
console.log(result1);
console.log(result2);

lastIndexOf()

• The usage of this method is the same as indexof()
• The difference is that indexOf() searches from the front to the back.
• And lastIndexOf() searches from the back to the front

slice()

• You can extract the specified content from the string
• It will not affect the original string, but will return the intercepted content
• parameter:
  • First, the index of the starting position (including the starting position)
  • Second, the index of the end position (not including the end position)
  • If the second parameter is omitted, all subsequent
  • You can also pass a negative number as a parameter, and if it is a negative number, it will be calculated from the back

var str = "Hello World!!!";
var result0 = str.slice(0,2);
var result1 = str.slice(1,-4);
console.log(result0);
console.log(result1);

substring()

• Can be used to intercept a string, similar to slice()
• It will not affect the original string, but will return the intercepted content
• parameter:
  • First, the index of the starting position (including the starting position)
  • Second, the index of the end position (not including the end position)
• Cannot accept negative values ​​as parameters
  • If a negative value is passed, 0 is used by default.
• Can automatically adjust the parameter position. If the second parameter is smaller than the first one, it will be automatically swapped.

var str = "Hello World!!!";
var result0 = str.substring(0,2);
console.log(result0);

split()

• You can split a string into an array
• parameter:
  • It takes a string as a parameter, and the array will be split according to the string.

var str = "He llo Worl d!!!";
var result0 = str.split(' ');
console.log(result0);
console.log(Array.isArray(result0));

toUpperCase()

• Converts a string to uppercase and returns

var str = "He llo Worl d!!!";
var result0 = str.toUpperCase();
console.log(result0);

toLowerCase()

• Converts a string to lowercase and returns

var str = "He llo Worl d!!!";
var result0 = str.toLowerCase();
console.log(result0);

Summarize

This article ends here. I hope it can be helpful to you. I also hope you can pay more attention to more content on 123WORDPRESS.COM!