What are the javascript reference data types?

There are three types of reference data types in JavaScript: 1. Object type, which is an unordered set of keys and values; 2. Array type, which is a set of sequential A collection of arranged data; 3. Function type, which 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.

Reference data types in JavaScript: Object, Array, Function.

1. Object type

The object type in JavaScript is an unordered set composed of keys and values. To define an object type, you need to Use curly braces { }, the syntax format is as follows:

{name1: value1, name2: value2, name3: value3, ..., nameN: valueN}

where name1, name2, name3,..., nameN are the keys in the object, value1, value2, value3,..., valueN are the corresponding values.

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, and the array can contain any type of data. To define an array in JavaScript, you need to use square brackets [ ]. Each element in the array is separated by commas, for example:

[1, 2, 3, 'hello', true, null]

In addition, you can also use the Array() function to create an array. , as shown in the following example:

var arr = new Array(1, 2, 3, 4);
console.log(arr);       // 输出 [1, 2, 3, 4]

Elements in the array can be accessed by index. Indexes in an array start at 0 and increase sequentially, that is, the first element of the array has index 0, the second element has index 1, the third element has index 2, and so on. As shown in the following example:

var arr = [1, 2, 3.14, 'Hello', null, true];
console.log(arr[0]);  // 输出索引为 0 的元素，即 1
console.log(arr[5]);  // 输出索引为 5 的元素，即 true
console.log(arr[6]);  // 索引超出了范围，返回 undefined

3. Function type

A function (Function) is a code block with a specific function. The function does not run automatically and needs to be passed The function name must be called 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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