JavaScript Foundation Fifth Day

First, Introduction

We discussed some of the basic concepts of the function, because the function is important in any language, so we should learn it well. When I opened my blog yesterday, I saw someone's private messages. My JavaScript was wrong, and I looked intently at the wrong words. I am sorry to say that, I hope you can see the time to spray me more than two words to forget this thing.

Second, import

Today we are going to talk about the content of the object, the first thing we want to touch is some built-in objects.

third, the key content

① object:

the list reads: "An unordered collection of attributes, each of which holds an original value, object, or function." Because There is no real class in JS, the class definition is described as the formula for the object. We also call the object definition class, because most developers are more familiar with the term, and functionally, the two are equivalent ""

② built-in objects:

Built-in objects are objects that the system has defined for us (similar to Math,Date,Array , and so on).

③math Object methods:

1) Math.ceil (): ceiling function, rounding up.

Console.log (Math.ceil (9.9));

2) Math.floor (); floor function, rounding down.

Console.log (Math.floor (9.9));

3) Math.Abs (); gets the absolute value of the number.

Console.log (Math.Abs (-9.9));

4) math.random (); Get 0-1 the random number.

Console.log (Math.random ());

5) Math.pow (); Get x of the y The power of the second.

Console.log (Math.pow (10,2));

6) Math.max (); gets the maximum value in two digits.

Console.log (Math.max (10,20));

7) math,min (); gets the minimum value in two digits.

Onsole.log (Math.min (10,20));

④date Object methods:

1) Conversion Date:

var New Date (2016,06,10); Console.log (date);

2) returns the number of milliseconds 1970 years 1 months 1 days midnight to a specified date (string).

var date = Date.parse ("2016-08-02") console.log (date);

3) milliseconds to get the date directly

1. 1. 1. in the HTML5 format

var date = date.now (); Console.log (date);

2. The recommended format

var date = +new  date (); Console.log (date) ;

4) Get the specified part of the date

1. 1. 1. 1. Returns a 4 -digit year

var year = date.getfullyear (); Console.log (year);

2. Return month starting from 0

var month = date.getmonth (); Console.log (month);

3. Return the day ordinal of the month

var day = date.getdate (); Console.log (day);

4. number of hours to return 0-23

var hours = date.gethours (); Console.log (hours);

5. Returns the minute number of 0-59

var minutes = date.getminutes (); Console.log (minutes);

6. number of seconds to return 0-59

var seconds =

7. Returns the same number of milliseconds as the valueOf () result

var Milliseconds = date.gettime (); Console.log (Milliseconds);

8. Returns the number of milliseconds

var Milliseconds = date.getmilliseconds (); Console.log (Milliseconds);

9. Return day of the week

var day = date.getday (); Console.log (day);

⑤array Object methods:

1) Slice method:Slice (start,end) [Start end](head does not take the tail)

1. 1. 1. When the value of end is positive:

Take from start , not end       

Console.log (Arr.slice (0,2));

2. When the value of end is negative:

If end is a negative number, the index is the length + negative number of the array

Console.log (Arr.slice (0,-2));

2) Convert an array:

1. 1. 1. ToString converts an array into a character turn.

Console.log (Arr.tostring ());  

2. ValueOf returns the array object itself

3) Gets the index of an element in the array

1. 1. 1. IndexOf returns the subscript of an array (where there are two elements)

A) one parameter:

Console.log (Arr1.indexof (1));

b) Two parameters: the second parameter specifies where to start the search

Console.log (Arr1.indexof);

4) Append and delete

1. 1. 1. Push (); added to the last face of the array.

Arr.push ("abc"); Console.log (arr); 

2. Pop (); deletes the last of the array.

Arr.pop (); Console.log (arr);

3. Shift (); deletes the first of the array.

Arr.shift (); Console.log (arr);

4. Unshift (); added to the front of the array.

Arr.unshift (1); Console.log (arr);

5) Array Sorting

1. 1. 1. Reverse (); flips the elements in the array.

Arr.reverse (); Console.log (arr);

2. Sort (); to sort the elements in an array

Arr.sort (function(b) { return A-b;}); Console.log (arr); 

6) Array Iteration

1. 1. 1. filter (); true Left, the return value is false the house.

var arr = arr.filter (function(element,inedx,num) { if(element<5) {  return true  }else{ returnfalse;}    }); console. log (arr);

2. ForEach (); facilitates every element in the loop array

var arr3= Arr.foreach (function(element,index,num) {    console.log (element);    Console.log (index);})

7) Array Empty

1. 1. 1. Array.splice (0,arr.length); Delete all items in the array
      2. array.length=0; Length can be read and copied, assigned to 0 empty array
      3. Array = []

8) manipulating arrays

1. 1. 1. Join () to string elements in an array by making a symbol

var arr4 = Arr.join ("|" ) Console.log (ARR4)

2. Concat (); Connect two arrays

var arr5 = arr.concat (arr2); Console.log (ARR5);

3. Slice intercepts a new array from the current array, without affecting the original array. Parameter start starting from 0 , end starting from 1 , end not intercepted.

var arr6 = Arr.slice (0,3) Console.log (ARR6);

4. Delete or replace some items of the current array, parameter start,deletecount,options ( the item to replace ),

var arr7 = Arr.splice (0,3); Console.log (ARR7);

⑥ String part:

1) Gets the index in the string:

1. 1. 1. Inidexof Returns the position of the specified content in the string

Console.log (Str.indexof ("W"));

2. LastIndexOf from behind, looking only for the first match .

Console.log (Str.lastindexof ("L"));

2) Remove blank:trim () only removes whitespace before and after the string

var str1 = "Hello World"console.log (STR1); Console.log (Str1.trim ());

3) string Conversion case:

1. 1. 1. Turn Capital touppercase ()

Console.log (Str.touppercase ()); 

2. Turn lowercase tolowercase ()

Console.log (Str.tolowercase ());

4) String manipulation methods:

1. 1. 1. Concat (); stitching strings, equivalent to + , + more commonly

Console.log (Str.concat (str1));

2. Slice (); from Start position to start, intercept to End location, End not be taken

Console.log (Str.slice (0,3));

3. substring (); from Start position to start, intercept to End location, End not be taken

Console.log (str.substring (0,3));  

4. substr (); from Start position start, intercept length characters, and only one parameter is truncated to the last

Console.log (Str.substr (0,4)); 

5. replace (); replaces an element of a string , and returns the replaced string

Console.log (Str.replace ("H", "H"));

6. Split (); splitting a string ( conversion ) Array

Console.log (Str.split (0,4));

7. The need to differentiate Yes is substring (); substr (); Slice ( )

A) when there is only one positive parameter:

is returned from the string following the start of the positive argument.

Console.log (Str.slice (1)), Console.log (Str.substr (1)), Console.log (str.substring (1));

b) When there is only one negative parameter:

console.log (str.slice (-1)); / Pass in a negative number, which is equivalent to passing in length + (-1), take it backwards, which is equivalent to taking two backwards
console.log (str.substr (-1)); Passing in a negative number is equivalent to passing in length + (-1) // intercepted backwards
console.log (str.substring (-1)); Pass in a negative number, which is equivalent to passing in 0, which is equivalent to all interception

c) When there are two positive parameters

console.log (str.slice (0,1)); take the specified index number
console.log (str.substr (0,1)); intercepts the specified number of characters
console.log (str.substring (0,1)); take the number of the index

D) When there is a positive and negative

console.log (str.slice (0, -1)); The second parameter is also equivalent to length + (-1)
console.log (str.substr (0, -1)); The second parameter, if the negative number is equal to 0, it cannot be intercepted, and it is empty
console.log (str.substring (1, -5)); The second parameter, if it is negative, is equivalent to 0, but this method will start from the smallest of the two parameters as the starting value 

Iv. Summary

Feel a little tired after summing up, I hope you can have some additions.

JavaScript Foundation Fifth Day