Learn more about built-in objects: reveal the definitions and characteristics of common built-in objects

Built-in Object Analysis: Explore the definitions and characteristics of common built-in objects

Introduction:
In programming languages, built-in objects refer to some provided by the programming language itself. Objects, which have special functions and properties that simplify writing code and provide more efficient operations. This article will introduce the definitions and characteristics of some common built-in objects, and give specific code examples.

1. Math object
The Math object is one of the built-in objects in the JavaScript language. It provides a series of methods and properties related to mathematical operations. Common Math object methods are:

1. Math.abs(x): Returns the absolute value of x.
2. Math.ceil(x): Returns the smallest integer greater than or equal to x.
3. Math.floor(x): Returns the largest integer less than or equal to x.
4. Math.random(): Returns a pseudo-random number between 0 and 1.
5. Math.max(x1, x2, ...): Returns the maximum value in a set of numbers.
6. Math.min(x1, x2, ...): Returns the minimum value in a set of numbers.

Code example 1:

let x = -10;
console.log(Math.abs(x)); // 输出：10

let y = 3.14159;
console.log(Math.ceil(y)); // 输出：4

let z = 4.9;
console.log(Math.floor(z)); // 输出：4

console.log(Math.random()); // 输出：0.123456789

let nums = [1, 2, 3, 4, 5];
console.log(Math.max(...nums)); // 输出：5
console.log(Math.min(...nums)); // 输出：1

2. Date object
The Date object is a built-in object used to process dates and times. It provides a series of date and time related methods and properties. Common Date object methods are:

1. Date.now(): Returns the number of milliseconds in the current time.
2. Date.parse(dateString): Convert date in string form to milliseconds.
3. Date.getFullYear(): Returns the year of the current date.
4. Date.getMonth(): Returns the month of the current date (0 means January, 11 means December).
5. Date.getDate(): Returns the date of the current date (starting from 1).
6. Date.getHours(): Returns the number of hours of the current time (24-hour format).

Code example 2:

console.log(Date.now()); // 输出：1612345678901

let dateStr = "2022/01/31";
console.log(Date.parse(dateStr)); // 输出：1643568000000

let currentDate = new Date();
console.log(currentDate.getFullYear()); // 输出：2022
console.log(currentDate.getMonth()); // 输出：0
console.log(currentDate.getDate()); // 输出：31
console.log(currentDate.getHours()); // 输出：15

3. String object
String object is a built-in object for processing strings. It provides a series of string-related methods and properties. . Common String object methods are:

1. length: Returns the length of the string.
2. charAt(index): Returns the character at the specified index.
3. concat(string1, string2, ...): Concatenate multiple strings.
4. indexOf(substring): Returns the index of the first occurrence of substring.
5. toUpperCase(): Convert the string to uppercase.
6. toLowerCase(): Convert the string to lowercase.

Code Example 3:

let str = "Hello, world!";
console.log(str.length); // 输出：13
console.log(str.charAt(4)); // 输出：o
console.log(str.concat(" Welcome")); // 输出：Hello, world! Welcome
console.log(str.indexOf("o")); // 输出：4
console.log(str.toUpperCase()); // 输出：HELLO, WORLD!
console.log(str.toLowerCase()); // 输出：hello, world!

Conclusion:
This article introduces common built-in objects, their definitions and characteristics, and provides specific code examples. The Math object is used for mathematical operations, the Date object is used for processing dates and times, and the String object is used for string processing. Understanding and mastering the use of these built-in objects can simplify code writing and improve program efficiency. Hope this article can be helpful to readers.

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