Built-in object analysis: definition and function of built-in objects

In-depth understanding of built-in objects: What are built-in objects and their functions, specific code examples are required

In JavaScript, built-in objects refer to some objects that come with the JavaScript language , they can be used directly anywhere without additional import or installation. These built-in objects provide a wealth of functions and methods to facilitate various operations and processing. Next, we will take an in-depth look at some commonly used built-in objects and give specific code examples.

1. Global Object

1. window object: The window object represents the browser window. It is the top-level object of JavaScript and provides many useful properties and methods, such as navigation and pop-up windows. , timing, etc. The following is a simple example:

// 弹出一个提示框 window.alert("Hello World!"); // 打开一个新窗口 window.open("https://www.example.com"); // 跳转到指定页面 window.location.href = "https://www.example.com";

2. Document object: The document object represents the document of the current web page, and it provides many methods and properties for manipulating HTML elements. For example, get elements, modify styles, add events, etc. The following is an example:

// 获取页面上的某个元素 var element = document.getElementById("myElement"); // 修改元素的样式 element.style.color = "red"; // 添加点击事件 element.addEventListener("click", function() { alert("Clicked!"); });

2. Data type object

1. String object: The String object is used to process strings, and it provides many common string operation methods. , such as interception, replacement, search, etc. The following is an example:

var str = "Hello World!"; // 获取字符串的长度 console.log(str.length); // 截取字符串的一部分 console.log(str.slice(0, 5)); // 替换字符串中的某个子串 console.log(str.replace("World", "JavaScript")); // 查找某个子串第一次出现的位置 console.log(str.indexOf("W"));

2. Array object: Array object is used to process arrays. It provides many common array operation methods, such as traversal, addition, deletion, modification, etc. The following is an example:

var arr = [1, 2, 3, 4, 5]; // 遍历数组 arr.forEach(function(item) { console.log(item); }); // 添加元素到数组的末尾 arr.push(6); // 修改数组中的某个元素 arr[0] = 0; // 查找某个元素在数组中的位置 console.log(arr.indexOf(3));

3. Date and time objects

1. Date object: The Date object is used to process dates and times. It provides many useful methods and Properties, such as getting the current time, formatting output, calculating time intervals, etc. The following is an example:

// 创建一个Date对象，表示当前时间 var now = new Date(); // 获取年份 console.log(now.getFullYear()); // 获取月份（注意返回的是0-11） console.log(now.getMonth() + 1); // 格式化输出日期 console.log(now.toDateString());

4. Math object

The Math object provides some commonly used mathematical functions and constants, such as exponentiation, rounding, absolute value, etc. The following is an example:

// 求2的3次幂 console.log(Math.pow(2, 3)); // 向下取整 console.log(Math.floor(3.7)); // 取绝对值 console.log(Math.abs(-5));

Summary:

In JavaScript, built-in objects provide a wealth of functions and methods to facilitate us to perform various operations and processing. Global objects, data type objects, date and time objects, and mathematical objects are commonly used built-in objects. By understanding these built-in objects and their functions, we can better use the JavaScript language for programming development and improve efficiency and development quality.

The above is some introduction and sample code about in-depth understanding of built-in objects. I hope it will be helpful to you. Through continuous learning and practice, we can further utilize the functions of built-in objects and write more powerful and reliable JavaScript programs.

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