


We have already used the prototype attribute in Chapter 1 to simulate the implementation of classes and inheritance. The prototype property is essentially a JavaScript object. And every function has a default prototype attribute.
If this function is used in the scenario of creating a custom object, we call this function a constructor. For example, a simple scenario below:
//Constructor
function Person(name) {
this.name = name;
}
// Define the prototype of Person. The attributes in the prototype can be referenced by custom objects
Person.prototype = {
getName: function() {
return this.name;
}
}
var zhang = new Person("ZhangSan");
console.log(zhang.getName() ); // "ZhangSan"
As an analogy, let's consider the data types in JavaScript - String, Number, Array, Object, Date (Date) etc. We have reason to believe that these types are implemented as constructors inside JavaScript, such as:
// Define the constructor of the array, as a predefined type of JavaScript
function Array() {
// ...
}
// Instance of initializing array
var arr1 = new Array(1, 56, 34, 12);
// However, we prefer the following syntax definition:
var arr2 = [1, 56, 34 , 12];
Many methods of operating on arrays at the same time (such as concat, join, push) should also be defined in the prototype attribute.
In fact, all intrinsic data types of JavaScript have read-only prototype attributes (this is understandable: because if the prototype attributes of these types are modified, the predefined methods disappear), but we can Add your own extension methods to it.
//Extend one to the JavaScript inherent type Array to get the minimum value Method of
Array.prototype.min = function() {
var min = this[0];
for (var i = 1; i if (this[i] min = this[i];
}
}
return min;
};
// on any instance of Array Call the min method
console.log([1, 56, 34, 12].min()); // 1
Note: There is a trap here, add it to the prototype of Array After the extension method, when using for-in to loop the array, this extension method will also be looped out.
The following code illustrates this (assuming that the min method has been extended to the Array prototype):
var arr = [1, 56, 34, 12];
var total = 0;
for (var i in arr) {
total = parseInt( arr[i], 10);
}
console.log(total); // NaN
The solution is also very simple:
var arr = [1, 56, 34, 12];
var total = 0;
for (var i in arr) {
if (arr.hasOwnProperty(i)) {
total = parseInt(arr[i], 10);
}
}
console .log(total); // 103

JavaScript is widely used in websites, mobile applications, desktop applications and server-side programming. 1) In website development, JavaScript operates DOM together with HTML and CSS to achieve dynamic effects and supports frameworks such as jQuery and React. 2) Through ReactNative and Ionic, JavaScript is used to develop cross-platform mobile applications. 3) The Electron framework enables JavaScript to build desktop applications. 4) Node.js allows JavaScript to run on the server side and supports high concurrent requests.

Python is more suitable for data science and automation, while JavaScript is more suitable for front-end and full-stack development. 1. Python performs well in data science and machine learning, using libraries such as NumPy and Pandas for data processing and modeling. 2. Python is concise and efficient in automation and scripting. 3. JavaScript is indispensable in front-end development and is used to build dynamic web pages and single-page applications. 4. JavaScript plays a role in back-end development through Node.js and supports full-stack development.

C and C play a vital role in the JavaScript engine, mainly used to implement interpreters and JIT compilers. 1) C is used to parse JavaScript source code and generate an abstract syntax tree. 2) C is responsible for generating and executing bytecode. 3) C implements the JIT compiler, optimizes and compiles hot-spot code at runtime, and significantly improves the execution efficiency of JavaScript.

JavaScript's application in the real world includes front-end and back-end development. 1) Display front-end applications by building a TODO list application, involving DOM operations and event processing. 2) Build RESTfulAPI through Node.js and Express to demonstrate back-end applications.

The main uses of JavaScript in web development include client interaction, form verification and asynchronous communication. 1) Dynamic content update and user interaction through DOM operations; 2) Client verification is carried out before the user submits data to improve the user experience; 3) Refreshless communication with the server is achieved through AJAX technology.

Understanding how JavaScript engine works internally is important to developers because it helps write more efficient code and understand performance bottlenecks and optimization strategies. 1) The engine's workflow includes three stages: parsing, compiling and execution; 2) During the execution process, the engine will perform dynamic optimization, such as inline cache and hidden classes; 3) Best practices include avoiding global variables, optimizing loops, using const and lets, and avoiding excessive use of closures.

Python is more suitable for beginners, with a smooth learning curve and concise syntax; JavaScript is suitable for front-end development, with a steep learning curve and flexible syntax. 1. Python syntax is intuitive and suitable for data science and back-end development. 2. JavaScript is flexible and widely used in front-end and server-side programming.

Python and JavaScript have their own advantages and disadvantages in terms of community, libraries and resources. 1) The Python community is friendly and suitable for beginners, but the front-end development resources are not as rich as JavaScript. 2) Python is powerful in data science and machine learning libraries, while JavaScript is better in front-end development libraries and frameworks. 3) Both have rich learning resources, but Python is suitable for starting with official documents, while JavaScript is better with MDNWebDocs. The choice should be based on project needs and personal interests.


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