JavaScript Learning notes (i)

Record methods and knowledge points to avoid late forgetting

null and undefined

NULL represents a null value, undefined represents a value not defined.

= = and = = =

= = The data type is automatically converted and then compared. = = = Does not automatically convert the data type and returns False if the data type is inconsistent.

For example: false = = 0:true,false = = = 0:false

Array

var = new Array (Arry);

var array = [n/a];

Object

var model = {

Name: "Chenxy",

Age:20

}

Json

var model = {
"Name": "Chenxy",
"Hooby": ["Eat", "Play", "Game"]
}

Strict mode and global variables

If the variable is not declared with Var, it is considered a global variable. If there are more than one global variable with the same name, it will conflict.

To fix this problem, roll out the strict mode, such as an undeclared exception. The starting method is to add ' use strict ' to the JS code;

Escape character

\ nthe line, \ t tab, \ \ is \

String method

var ToUpper = strtext.touppercase ();    Console.log ("all capitalization:" +ToUpper);     var ToLower = strtext.tolowercase ();    Console.log ("all lowercase:" +ToLower);     var IndexOf = Strtext.indexof ("JQ");    Console.log ("returns the position where the specified character appears, if not-1:" +IndexOf)    ; var SUBSTR = strtext.substring (0,3);    Console.log ("returns the specified interval string:" +substr);

Array method

vararr = [10,20,30, ' 40 ']; varIndexOf = Arr.indexof (20); Console.log ("Returns the specified index if it is not-1:" +IndexOf); varSlice = Arr.slice (2,3); Console.log ("Intercepts some elements, returns a new array, and if you do not write the second one, the default is truncated to the last:" +Slice); Arr.push (50,60);//add several elements to the endArr.unshift (5,6);//add several elements to the headArr.pop ();//Delete last elementArr.shift ();//Delete First elementArr.sort ();//SortArr.reverse ();//ReverseArr.splice (2,3,80,90);//Delete three elements starting at index 2 and add two elements        varARR2 = [' A ', ' B ', ' C ']; Arr.concat (ARR2); //merging two arraysArr.concat (1,2,[3,4]);//automatically take the array apart and combine        varJoin = Arr.join ('-')); Console.log ("Each element is connected with the specified connector:" +join);

In operator

Queries whether an object contains a property. Contains true, and vice versa is false.

Example: ' name ' in obj;

Map and set

The structure of a set of key-value pairs with extremely fast lookup speeds. The key can not be the same name, if the same name will replace the previous

var New // initializing an empty map    // Add a    Smap.set ("B", +);    Smap.has (// to determine if there is    // get the corresponding value    sMap.  Delete// Remove key

The set does not have duplicate keys, and the repeating elements are automatically filtered. The rest is the same as map.

Arguments

All parameters that were passed in by the caller. Just write it in the direct way.

Rest

The extra arguments are given to the variable rest in the form of an array. Example: Function A (A, B,.. Rest) {}

This

Gets only the object that was called.

Apply to fix this point to object. Two parameters, the first one is the this variable that needs to be bound, and the second is the parameter. Example: Geta.apply (xiaoming,[1,2,3]); This points to xiaoming with a parameter of 123

Call is similar to apply, but is sequential input. Geta.call (xiaoming,1,2,3);

Decorative Device

With apply, you can rewrite the window's built-in methods. Example:

var oldparint = window.parseint;     function () {        alert (1);         return oldparint.apply (null,arguments);    }

Map

Iterating over an array allows each element in the array to execute a method. Cases:

function POW (x)    {        return x*x;    }     var arr = [1,2,3,4,5,6];    Arr.map (POW);

Reduce

The function must receive two values, iterate over the array, and perform an accumulative calculation. Cases:

function pow (x, y)    {        return x*y;    }     var arr = [1,2,3,4,5,6];    Arr.reduce (POW);

JavaScript Learning notes (i)