Javascript_javascript スキルの最初の概要の概要

1.HTML 内のスクリプトは、<script> タグと </script> の間に配置する必要があります。

スクリプトは HTML ページの セクションに配置できます

2. JavaScript から HTML 要素にアクセスするには、 document.getElementById(id) メソッドを使用できます

3. document.write() を通じて、タグを含むコンテンツを HTML ドキュメントに書き込むことができます。ドキュメントがロードされた後に document.write() が実行されると、HTML ドキュメント全体が上書きされることに注意してください

4.JS は 2 つの方法でアノテーションを付けます: // と /**/

5. 変数は var を通じて宣言されます。JS は弱い型指定言語であるため、変数の型を指定する必要はありません。

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7.var num=new Number()//Declare a Number object

Number.MAX_VALUE Maximum value
Number.MIN_VALUE Minimum value
Number.NaN special non-numeric value
Number.NEGATIVE_INFINITY Negative infinity
Number.POSITIVE_INFINITY Positive infinity
Number.toExponential() Format numbers using exponential notation
Number.toFixed( ) uses fixed-point counting to format numbers
Number.toLocaleString() Converts numbers into local format strings
Number.toPrecision() Format the significant digits of the number
Number.toString( ) Converts a number into a string
Number.valueOf( ) returns the original value
8.var str = new String() //Declare a string object

str.substr(start,length): Extract and return a substring in str. But it does not modify str. start indicates the starting position of extraction, and length indicates the length. If length is omitted, it indicates extraction to the end.

str.substring(from,to): will return the substring of the string string, consisting of the characters from from to to, including the characters located in from, excluding the characters located in to. If from>to, that is Intercepted after automatic replacement.

　Str.toLowerCase(): Convert the string to lowercase

　Str.toUpperCase(): Convert the string to uppercase

str.split(): Split the string according to the specified symbol

str.slice(): Same as substring() but more flexible, allowing negative values, similar to Array.slice()

str.concat(): String link, similar to Array.concat, but it is more convenient to use numbers

Str.indexOf(): Retrieve characters and return the position where the character first appears

9.var date=new Date() //Create a date object

Main methods:

Date.get/setDay() //Return/set a day of the week (0~6),

Date.get/setFullYear() // Return/set the year in system time

Date.get/setMonth() // Return/set the month field (0~11) in system time

date.get/setDate() //Return/set a certain day of the month

Date.get/setHours() // Return/set the hour field in the system time

Date.get/setMinutes() // Return/set the minutes field in the system time

Date.get/setSeconds() // Return/set the seconds field in the system time

Date.get/setTime() //Return/Set//Return/Set the minute field in the system time

10.var arr=new Array() //Create an array object

Main attributes: arr.length //Returns the length of the array

Main methods:

pop() //Delete and return the last element of the array, the return value is the deleted element

push() //Add elements to the end of the array and return the length of the array

shift()　 //Move the first element out of the array, and the return value is the deleted element

unshift()　　//Insert an element at the head of the array and return the length of the array

　slice()　　　//Return a part of the array, the parameter can be a negative value, return the intercepted array

Reverse() //Reverse the order in the array and return the reversed array

sort()　 //To sort array elements, you need to specify a method

concat()　 //Array connection, returns the connected array without changing the original array

join()　　//Join the array elements with the specified characters and return them in string form

splice() //Insert, delete or replace elements of the array,

toString() //Convert the array into a string

11.Math is a native object

Math.abs() //Return the absolute value

Math.ceil() // Round up

Math.floor() // Countryside rounding

Math.round() // Rounding up

Math.randow() // Returns a random number

Math.max() // Return the larger value

Math.min() // Return the smaller value

Math.PI() //Constant PI

Math.pow() // x to the y power

Math.sqrt() // Calculate the square

12. Others

isNaN() // Determine whether it is a numerical value. If not, return true

parseInt() // Forced conversion to integer type

parseFloat() // Forced conversion to floating point value

alert() // Warning

confirm()　 //Message confirmation box

prompt()　　//Prompt message box

Document.write() //Write content to the HTML document. If the document content is loaded and written using this method, the entire HTML document will be overwritten

　document.getElementById()　//Get the object by ID name

　document.getElementsTagName()　//Get the object through the tag name and return an array object

　document.getElementsClassName()　//Get the object through the class name and return an array object

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