What are the javascript composite data types?

javascript composite data type: 1. Object type, which is an unordered collection of keys and values; 2. Array type, which is a collection of ordered data. Each member of the array is It is called an element, and the name of each element is called an array subscript; 3. Function type is a block of code with a specific function.

The operating environment of this tutorial: windows7 system, javascript version 1.8.5, Dell G3 computer.

Data types in JavaScript can be divided into two types:

• Basic data types (value types): String, Number, Boolean, Null, Undefined, Symbol;

• Reference data type (composite data type): Object ), array (Array), function (Function).

JavaScript composite data type

1. Object type

Object data type, called an object, is an unordered set of keys and values. It can be created using the new operator followed by the name of the object type to be created. Can also be created using literal notation. Add a property with a different name (any string including the empty string).

1) Constructing an object

Use the new operator to call the constructor to construct an instance object. The specific usage is as follows:

var objectName = new functionName(args);

Parameter description is as follows:

• objectName: the returned instance object.

• functionName: Constructor, basically the same as an ordinary function, but does not need to return a return value and returns an instance object, which can be accessed in advance using this within the function.

• args: Instance object initialization configuration parameter list.

Example

The following example uses different types of constructors to define various instances.

var o = new Object(); //Define an empty object

var a = new Array(); //Define an empty array

var f = new Function(); //Define an empty function

2) Object direct quantity

Using direct quantity can quickly create objects, which is also the most efficient and simplest method. The specific usage is as follows:

var objectName = {
    属性名1 : 属性值1,
    属性名2 : 属性值2,
    ...
    属性名n : 属性值n
};

In object literals, the attribute name and attribute value are separated by colons. The attribute value can be any type of data, and the attribute name can be a JavaScript identifier or a string. type expression. Properties are separated by commas, and no comma is required at the end of the last property.

In JavaScript, the keys of object types are all string types, and the values ​​can be of any data type. To get a value in an object, you can use the form of object name.key, as shown in the following example:

var person = {
    name: 'Bob',
    age: 20,
    tags: ['js', 'web', 'mobile'],
    city: 'Beijing',
    hasCar: true,
    zipcode: null
};
console.log(person.name);       // 输出 Bob
console.log(person.age);        // 输出 20

2, Array type

Array (Array) It is a collection of data arranged in order. Each value in the array is called an element (Element), and the name (key) of each element is called an array index (Index). The length of the array is flexible and readable and writable.

Arrays can contain any type of data.

There are two ways to define (create or declare) an array in JavaScript: constructed array and array literal.

1) Constructing an array

When you use the new operator to call the Array() type function, you can construct a new array.

Example:

• Call the Array() function directly without passing parameters to create an empty array.

var a = new Array();  //空数组

• Passing multiple values ​​creates a real array.

var a = new Array(1, true, "string", [1,2], {x:1,y:2});  //实数组

Each parameter specifies the value of an element, and there is no limit on the value type. The order of parameters is also the order of array elements, and the length property value of the array is equal to the number of parameters passed.

• Pass a numeric parameter to define the length of the array, that is, the number of elements it contains.

var a = new Array(5);  //指定长度的数组

The parameter value is equal to the attribute value of the array length, and the default value of each element is undefined.

• If you pass an argument with a value of 1, JavaScript will define an array of length 1 instead of an array containing one element with a value of 1.

var a = new Array(1);
console.log(a[0]);

2) Array literal

The syntax format of array literal: Contain multiple value lists in square brackets, separated by commas.

The following code uses array literals to define arrays.

var a = [];  //空数组
var a = [1, true, "0", [1,0], {x:1,y:0}];  //包含具体元素的数组

It is recommended to use array literals to define arrays, because array literals are the easiest and most efficient way to define arrays.

3. Function type

A function (Function) is a block of code with a specific function. The function does not run automatically and needs to be called through the function name to run. As shown in the following example:

function sayHello(name){
    return "Hello, " + name;
}
var res = sayHello("Peter");
console.log(res);  // 输出 Hello, Peter

In addition, functions can also be stored in variables, objects, and arrays, and functions can also be passed as parameters to other functions, or returned from other functions, as shown in the following example:

var fun = function(){
    console.log("http://c.biancheng.net/js/");
}
function createGreeting(name){
    return "Hello, " + name;
}
function displayGreeting(greetingFunction, userName){
    return greetingFunction(userName);
}
var result = displayGreeting(createGreeting, "Peter");
console.log(result);  // 输出 Hello, Peter

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