Summary of jQuery data types (14)_jquery

In addition to the built-in datatypes in native JS, jQuery also includes some extended data types (virtual types), such as Selectors, Events, etc.

1. String

String is the most common and is supported by almost any high-level programming language and scripting language. For example, "Hello world!" is a string. The type of string is string. For example

var typeOfStr = typeof "hello world";//typeOfStr is "string"

1.1 String built-in methods

"hello".charAt(0) // "h"
"hello".toUpperCase() // "HELLO"
"Hello".toLowerCase() // "hello"
"hello".replace(/e|o/g, "x") // "hxllx"
"1,2,3".split(",") // ["1", "2", "3"]

1.2 length attribute: returns the character length, for example, "hello".length returns 5

1.3 Convert string to Boolean:

An empty string ("") defaults to false, while a non-empty string defaults to true (such as "hello").

2. Number

Number type, such as 3.1415926 or 1, 2, 3...

typeof 3.1415926 returns "number"

2.1 Number converted to Boolean:

If a Number value is 0, it defaults to false, otherwise it is true.

2.2 Since Number is implemented using double-precision floating point numbers, the following situation is reasonable:

0.1 + 0.2 // 0.30000000000000004

3. Math

The following method is similar to the static method of Math class in Java.

Math.PI // 3.141592653589793
Math.cos(Math.PI) // -1

3.1 Convert strings to numbers: parseInt and parseFloat methods:

parseInt("123") = 123 (using decimal conversion)
parseInt("010") = 8 (using octal conversion)
parseInt("0xCAFE") = 51966 (using hexadecimal conversion)
parseInt("010", 10) = 10 (specify decimal conversion)
parseInt("11", 2) = 3 (specify binary conversion)
parseFloat("10.10") = 10.1

3.2 Number to string

When you append Number to the string, you will get the string.
"" + 1 + 2; // "12"
"" + (1 + 2); // "3"
"" + 0.0000001; // "1e-7"
Or use forced type conversion:
String(1) + String(2); //"12"
String(1 + 2); //"3"

4. NaN and Infinity

If the parseInt method is called on a non-numeric string, NaN (Not a Number) will be returned. NaN is often used to detect whether a variable is of numeric type, as follows:

isNaN(parseInt("hello", 10)) // true
Infinity represents an infinitely large or infinitely small value, such as 1 / 0 // Infinity.

Calling the typeof operator on both NaN and Infinity returns "numuber".

Also NaN==NaN returns false, but Infinity==Infinity returns true.

5. Integer and Float

It is divided into integer type and floating point type.

6. BOOLEAN

Boolean type, true or false.

7. OBJECT

Everything in JavaScript is an object. Performing a typeof operation on an object returns "object".

var x = {}; 
var y = { name: "Pete", age: 15 };

For the above y object, you can use dots to obtain attribute values. For example, y.name returns "Pete" and y.age returns 15

7.1 Array Notation (array access method to access objects)

var operations = { increase: "++", decrease: "--" } 
var operation = "increase"; 
operations[operation] // "++"; 
operations["multiply"] = "*"; // "*"

The above operations["multiply"]="*"; adds a key-value pair to the operations object.

7.2 Object loop access: for-in

var obj = { name: "Pete", age: 15}; 
for(key in obj) { 
alert("key is "+[key]+", value is "+obj[key]); 
}

7.3 Any object, regardless of whether it has attributes or values, defaults to true

7.4 Prototype attribute of object

Use fn (alias of Prototype) in jQuery to dynamically add objects (functions) to jQuery Instances

var form = $("#myform"); 
form.clearForm; // undefined 
form.fn.clearForm = function() {
return this.find(":input").each(function() { this.value = ""; }).end();
}; 
form.clearForm() // works for all instances of jQuery objects, because the new method was added

8. OPTIONS

Almost all jQuery plug-ins provide an API based on OPTIONS. OPTIONS is a JS object, which means that the object and its properties are optional. Allow customization.
For example, using Ajax to submit a form,

$("#myform").ajaxForm();//By default, the Action attribute value of the Form is used as the Ajax-URL, and the Method value is used as the submission type (GET/POST)
$("#myform").ajaxForm({ url: "mypage.php", type: "POST" }); // Covers the submitted URL and submission type

9. ARRAY

var arr = [1, 2, 3];

ARRAY is a variable list. ARRAY is also an object.

Read or set the value of an element in ARRAY, using this method:

var val = arr[0];//val为1
arr[2] = 4;//现在arr第三个元素为4

9.1 Array loop (traversal)

for (var i = 0; i < a.length; i++) { // Do something with a[i] }
但是当考虑性能时，则最好只读一次length属性，如下：
for (var i = 0, j = a.length; i < j; i++) { // Do something with a[i] }
jQuery提供了each方法遍历数组：
var x = [1, 2, 3]; 
$.each(x, 
function(index, value) { 
console.log("index", index, "value", value); 
});

9.2 Calling the push method on an array means adding an element to the end of the array, such as x.push(5); and x.[x.length] = 5; are equivalent

9.3 Other built-in methods of arrays:

var x = [0, 3, 1, 2]; 
x.reverse() // [2, 1, 3, 0] 
x.join(" – ") // "2 - 1 - 3 - 0" 
x.pop() // [2, 1, 3] 
x.unshift(-1) // [-1, 2, 1, 3] 
x.shift() // [2, 1, 3] 
x.sort() // [1, 2, 3] 
x.splice(1, 2) // 用于插入、删除或替换数组元素，这里为删除从index=1开始的2个元素

9.4 数组为对象，所以始终为true

10. MAP

The map type is used by the AJAX function to hold the data of a request. This type could be a string, an array<form elements>, a jQuery object with form elements or an object with key/value pairs. In the last case, it is possible to assign multiple values to one key by assigning an array. As below:
{'key[]':['valuea','valueb']}

11. FUNCTION:匿名和有名两种

11.1 Context、Call和Apply

In JavaScript, the variable "this" always refers to the current context. 
$(document).ready(function() { 
// this refers to window.document}); 
$("a").click(function() { // this refers to an anchor DOM element
});

12. SELECTOR

There are lot of plugins that leverage jQuery's selectors in other ways. The validation plugin accepts a selector to specify a dependency, whether an input is required or not:
emailrules: { required: "#email:filled" }
This would make a checkbox with name "emailrules" required only if the user entered an email address in the email field, selected via its id, filtered via a custom selector ":filled" that the validation plugin provides.

13. EVENT

DOM标准事件包括：blur, focus, load, resize, scroll, unload, beforeunload, click, dblclick, mousedown, mouseup, mousemove, mouseover, mouseout, mouseenter, mouseleave, change, select, submit, keydown, keypress, andkeyup

14. JQUERY

JQUERY对象包含DOM元素的集合。比如$('p')即返回所有e388a4556c0f65e1904146cc1a846bee...94b3e26ee717c64999d7867364b1b4a3
JQUERY对象行为类似数组，也有length属性，也可以通过index访问DOM元素集合中的某个。但是不是数组，不具备数组的某些方法，比如join()。

许多jQuery方法返回jQuery对象本身，所以可以采用链式调用：
$("p").css("color", "red").find(".special").css("color", "green");
但是如果你调用的方法会破坏jQuery对象，比如find()和filter()，则返回的不是原对象。要返回到原对象只需要再调用end()方法即可。