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Detailed explanation of steps to use JS string method

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php中世界最好的语言Original
2018-05-24 16:07:402199browse

This time I will bring you a detailed explanation of the steps to use the JSstring method, and what are the notes when using the JS string method. The following is a practical case, let's take a look.

1. Method reading instructions

Return value typeObject.Method name (parameter 1[, parameter two]);
Explanation:

返回值类型:指的是函数调用结束后返回的值的类型。
对象.方法名称:指的是调用方法。
参数列表:表示函数调用时传入的参数。[]表示可选参数,可写可不写。

2. String attribute

Definition: By a pair of "" or a pair of '' Wrapped, it is a string composed of 0 or more characters .
String length:

string.length;

eg:

var str1="abc";
var str2="";
var str3=" ";
console.log(str1.length);//3
console.log(str2.length);//0
console.log(str3.length);//1

3.charAt

Function: This method returns the character at the corresponding position of .
Syntax: string string.charAt(index);
Parameters: index refers to 0 to string length-1 is an integer.
Return value: Returns the character at the corresponding position of the string.

Note:

- 如果传入参数小于0或者大于 字符串长度-1,则返回空字串。
- 如果传入boolean值,如果为true,默认是转化为数字1,指到字符串第二个字符。如果为false,默认是转化为数字0,指到字符串第一个字符。
- 如果传入任意字符串,则指到字符串第一个字符。
<script>
        var str="abc";
        console.log(str.charAt(0));//a
        console.log(str.charAt(2));//c
        console.log(str.charAt(-88));//""
        console.log(str.charAt(false));//a
        console.log(str.charAt(true));//b
        console.log(str.charAt("unm"));//a
</script>

4.chatCodeAt

Function: Returns the Unicode value of the character corresponding to
Syntax: number string.charCodeAt(index);
Parameters: index refers to 0 to string length-1 is an integer.
Return value: Returns the Unicode value of the character at the corresponding position in the string.

Note:
If the incoming parameter is less than 0 or is greater than the string length -1, an empty string will be returned. NAN is returned.

<script>
    var str="abc";
    console.log(str.charCodeAt(0));//97
    console.log(str.charCodeAt(2));//99
    console.log(str.charCodeAt(-88));//NAN
    console.log(str.charCodeAt(false));//97
    console.log(str.charCodeAt(true));//98
    console.log(str.charCodeAt(undefined));//97
    console.log(str.charCodeAt("zzzz"));//97
</script>

4.fromCharCode

Function: Convert Unicode values ​​into corresponding characters.
Syntax: string String.fromCharCode(index);
Parameters: index refers to passing in any integer.
Return value: Returns the string corresponding to the Unicode value.

<script>
    console.log( String.fromCharCode( 97 ) );//a
    console.log( String.fromCharCode( 65 ) );//A
</script>

Small example of encryption and decryption

5.indexOf

Function: Returns the specified value string when calling this methodFirst timeThe position where it appears.
Syntax: number string.indexOf((searchValue [, fromIndex]));
Parameters: searchValue refers to The string to find. fromIndex refers to where to start searching. The default value is 0.
Return value: Returns a number.
Note: If it exists, the position will be returned, if it does not exist, -1 will be returned.

<script>
    var str="abcabcabc";
    console.log(str.indexOf("a"));//0
    console.log(str.indexOf("b"));//1
    console.log(str.indexOf("z"));//-1
    console.log(str.indexOf("ab"));//0
    console.log(str.indexOf("ac"));//-1
    console.log(str.indexOf("bc",0));//1
    console.log(str.indexOf("bc",-2));//1
    console.log(str.indexOf("bc",18));//-1
</script>

5.lastIndexOf

Function: Returns the specified value where the last of the string appears when this method is called.
Syntax: number string.indexOf((searchValue [, fromIndex]));
Parameters: searchValue refers to The string to find. fromIndex refers to where to start searching. The default value is str.length-1.
Return value: Returns a number.
Note: If it exists, the position will be returned, if it does not exist, -1 will be returned.

<script>
        var str="abcabcabc";
        console.log(str.lastIndexOf("a"));//6
        console.log(str.lastIndexOf("b"));//7
        console.log(str.lastIndexOf("z"));//-1
        console.log(str.lastIndexOf("ab"));//6
        console.log(str.lastIndexOf("ac"));//-1
        console.log(str.lastIndexOf("bc",0));//-1
        console.log(str.lastIndexOf("bc",-2));//-1
        console.log(str.lastIndexOf("bc",18));//7
</script>

6.slice

Function: method extracts a part of the string and returns this new string (including the starting position, not including End position)
Syntax: string string.slice((star [, end]));
Parameters: star is Refers to the interception starting position , end refers to the interception end position , the default is position 1 of the last character (the length of the string).
Return value: Return the intercepted string.

Note:

  • will not exchange parameter positions according to parameter size

  • If there are Negative values ​​are processed from the end. -1 refers to the last element, -2 refers to the penultimate element.

<script>
    var str="abcabc";
    console.log(str.slice(2));//"cabc"
    console.log(str.slice(0,2));//"ab"
    console.log(str.slice(2,2));//""
    console.log(str.slice(2,-1));//"cab"
    console.log(str.slice(2,-6));//""
    console.log(str.slice(2,1));//""
    console.log(str.slice(-2,-1));//"b"
</script>

7.substring

作用: 方法提取字符串中的一部分,并返回这个新的字符串(包含起始位置,不包含结束位置)
语法: string string.slice((star [, end]));
参数: star是指截取的起始位置,end是指截取的结束位置,默认为最后一个字符的位置+1 ( 字符串的长度 )。
返回值:  返回 截取后的字符串。

注意:

  • 会根据起始位置和结束位置的大小先进行参数位置的变换

  • 会把负值转换成0

<script>
    var str="abcabc";
    console.log(str.substring(2));//"cabc"
    console.log(str.substring(0,2));//"ab"
    console.log(str.substring(2,2));//""
    console.log(str.substring(2,-1));//"ab"
    console.log(str.substring(2,-6));//"ab"
    console.log(str.substring(2,1));//"b"
    console.log(str.substring(-2,-1));//""
</script>

8.substr

作用: 截取指定 起始位置长度子字符串.
语法: string string.substr(start [, length]);
参数: start :截取的起始位置 。length:截取的字符串长度,默认为字符长度。
返回值: 返回截取后的字符串

<script>
    var str="abcabcabcabc";
    console.log(str.substr(0));//abcabcabcabc
    console.log(str.substr(3));//abcabcabc
    console.log(str.substr(3,5));//abcab
    console.log(str.substr(3,-1));""
</script>

9.toLowerCase

1.toLowerCase
作用: 把字符串全部转成小写
语法: string string.toLowerCase();
返回值: 返回转成小写的字符串。

2.toUpperCase
作用: 把字符串全部转成大写
语法: string string.toUpperCase();
返回值: 返回转成大写的字符串。

<script>
        var str = "liangZhiFANG";
        console.log( str.toLowerCase() );//"liangzhifang"
        console.log( str.toUpperCase() );//"LIANGZHIFANG"
        console.log( str );//"liangZhiFANG"
        console.log( "LoveJs".toLowerCase() );//"lovejs"
</script>

10.split

作用: 通过一个指定的字符串 把原字符串分割成一个数组
语法: array string.split([separator] [, limit])
参数:separator是指分割符。limit指定最多分割的数量,可以理解为数组长度,默认为全部。
返回值:返回一个数组。
注意:没有分割符的时候(没有传入参数),整个字符串将作为一个整体保存到数组中。 用分割符分割的时候,分割符会在被删除了在传入数组。

<script>
        var str="我爱,你,们";
        console.log(str.split(","));//["我爱","你","们"]
        console.log(str.split(",",2));//["我爱","你"]
        console.log(str.split());//["我爱,你,们"]
        console.log(str.split("mmm"));//["我爱,你,们"]
        console.log(str.split(""));//["我", "爱", "," , "你", "," ,"们"]
    </script>

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