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JavaScript is an object-oriented, dynamic, weakly typed programming language. It is widely used in web development. It has good interactivity and flexibility and can be combined with HTML and CSS to develop high-quality dynamic web pages. JavaScript has the concept of attributes, which are values that describe the characteristics of an object. This article will introduce the basic properties of JavaScript.
The length property is used to get the length of a string or array. For strings, the length property returns the number of characters in the string, while for arrays, the length property returns the number of elements in the array.
For example, we can use the length attribute to get the length of a string:
var str = "hello world"; var len = str.length; console.log(len); //输出:"11"
In addition, we can also use the length attribute to get the length of an array:
var arr = [1,2,3,4,5]; var len = arr.length; console.log(len); //输出:"5"
The prototype property is a unique property of the function object. It is a pointer to the prototype object. Every JavaScript function has a prototype attribute, whether it is a built-in function or a custom function.
For example, we can define a Person function and define a sayHello method in its prototype attribute:
function Person(name) { this.name = name; } Person.prototype.sayHello = function() { console.log("Hello, my name is " + this.name); }
Then, we can create a Person instance and call the sayHello method:
var person = new Person("John"); person.sayHello(); //输出:"Hello, my name is John"
The constructor attribute is a reference to the constructor function. When we create an object, it automatically adds a constructor attribute pointing to the constructor that created the object.
For example, we can create an object with a custom constructor and get its constructor property:
function Car(make, model) { this.make = make; this.model = model; } var myCar = new Car("Toyota", "Camry"); console.log(myCar.constructor); //输出:Car(make, model)
var num = new Number(10); var str = num.toString(); console.log(str); //输出:"10"
For example, we can use the valueOf() method to convert a numeric type object into a primitive numeric type:
var num = new Number(10); var val = num.valueOf(); console.log(val); //输出:10Object.prototype property
var obj = {name:"John", age:30}; var str = Object.prototype.toString.call(obj); console.log(str); //输出:"[object Object]"SummaryIn JavaScript, a property is a A value that describes an object's properties. Common JavaScript basic properties include: length, prototype, constructor, toString() method, valueOf() method and Object.prototype property, etc. Mastering these properties is very helpful for in-depth understanding of the basics of the JavaScript language.
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