String of JavaScript series (I)

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： character
• Whether 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 index UTF-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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