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String of JavaScript series (I)
2021-08-27 04:47:16 【Cooked fish】
This is my participation 8 The fourth of the yuegengwen challenge 23 God , Check out the activity details :8 Yuegengwen challenge
One 、 Search judgment
1.1 charAt
charAt()
Method returns the specified character from a string .
str.charAt(index)
@params
: A between 0 And string length minus 1 Integer between . (0~length-1), Default 0.@return
: characterWhether to change the original string
: Don't change
const str = 'hello';
console.log(str.charAt(2)); // 'e'
console.log(str.charAt(5)); // ''
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1.2 charCodeAt
charCodeAt()
Method returns 0 To 65535 Integer between , Represents... At a given indexUTF-16
Code unit .
str.charCodeAt(index)
@params
: A greater than or equal to 0, An integer less than the length of the string . If it's not a value , The default is 0.@return
: Appoint index Character at UTF-16 A number of code unit values ; If index Out of range ,charCodeAt() return NaN.Whether to change the original string
: Don't change
const str = 'hello';
console.log(str.charCodeAt(2)); // 108
console.log(str.charCodeAt(5)); // NaN
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1.3 indexOf
indexOf()
Method returns the... That called it String The index of the specified value for the first time in an object , from fromIndex Search for . If the value is not found , Then return to -1.
str.indexOf(searchValue [, fromIndex])
@params
:- searchValue: Is the string value to be looked up ;
- fromIndex: Indicates where to start the search . It can be any integer , The default value is 0.
@return
: String to find searchValue The index of the first occurrence of , If not found , Then return to -1.Whether to change the original string
: Don't change
console.log('Blue Whale'.indexOf('Blue')) // return 0
console.log('Blue Whale'.indexOf('Blute')) // return -1
console.log('Blue Whale'.indexOf('Whale', 0)) // return 5
console.log('Blue Whale'.indexOf('Whale', 5)) // return 5
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1.4 lastIndexOf
lastIndexOf()
Method returns the call String The index of the last occurrence of the specified value of the object , The specified position in a string fromIndex Search from back to front . If the specified value is not found, return -1 .
str.lastIndexOf(searchValue[, fromIndex])
@params
:- searchValue: Is a string , Represents the value being looked up . If searchValue Is an empty string , Then return to fromIndex.;
- fromIndex: Optional , String to match searchValue The first character of is from str Of the fromIndex Bits start looking back to the left .
@return
: Returns the index of the last occurrence of the specified value ( The index is still left to right 0 Start counting ), If not, return -1.Whether to change the original string
: Don't change
const str = 'Brave new world';
console.log(str.lastIndexOf('w'));
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1.5 startsWith
startsWith()
Method is used to determine whether the current string begins with another given substring , And according to the judgment result returns true or false.
str.startsWith(searchString[, position])
@params
:- searchString: Represents the substring to search ;
- position: Optional , It means that str Mid search searchString The beginning of , The default value is 0.
@return
: If the given character is found at the beginning of the string, it returns true; Otherwise return to false.Whether to change the original string
: Don't change
const str = 'Saturday night plans';
console.log(str.startsWith('Sat')); // true
console.log(str.startsWith('Sat', 3)); // false
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1.6 endsWith
endsWith()
Method is used to determine whether the current string is a given substring “ ending ” Of , Return according to the judgment result true or false.
str.endsWith(searchString[, length])
@params
:- searchString: Represents the substring to search ;
- length: Optional , yes str The length of . The default value is str.length.
@return
: Returns... If the passed in substring is at the end of the search string true, Otherwise it will return false.Whether to change the original string
: Don't change
const str = 'To be, or not to be, that is the question.';
console.log(str.endsWith('question.')); // true
console.log(str.endsWith('to be')); // false
console.log(str.endsWith('to be', 19)); // true
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1.7 includes
includes()
Method is used to determine whether a string is contained in another string , Return according to the situation true or false.
str.includes(searchString[, position])
@params
:- searchString: Represents the string to search in this string
- position: Optional , Indicates which index position of the current string to start searching for substrings , The default value is 0.
@return
: If the current string contains the searched string , Just go back to true; Otherwise return to false.Whether to change the original string
: Don't change
const str = 'To be, or not to be, that is the question.';
console.log(str.includes('To be')); // true
console.log(str.includes('question')); // true
console.log(str.includes('nonexistent')); // false
console.log(str.includes('To be', 1)); // false
console.log(str.includes('TO BE')); // false
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1.8 localeCompare
localeCompare()
Method returns a number indicating whether a reference string is before or after the sort order or is the same as the given string .
referenceStr.localeCompare(compareString[, locales[, options]])
@params
:- compareString: Represents the string used for comparison ;
- locales: Optional , A term used to represent one or more languages or regions BCP 47 A standard string or an array of strings .
- options: Optional .
@return
: If the reference character exists before the comparison character, it is a negative number ; If the reference character exists after the comparison character, it is a positive number ; Return when equal 0.Whether to change the original string
: Don't change
console.log('a'.localeCompare('c')); // -1
console.log('check'.localeCompare('against')); // 1
console.log('a'.localeCompare('a')); // 0
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copyright notice
author[Cooked fish],Please bring the original link to reprint, thank you.
https://en.qdmana.com/2021/08/20210827044712699O.html
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