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Common methods for JavaScript built-in String objects

Creating a string

  • var str = "hello world";

Get the length of the string

  • str.length

charAt()

  • Purpose: Get the character of the specified index of the string
  • Grammar:str.charAt(index)
  • indexValues for0 到 str.length - 1Negative numbers are not supported
  • Reference: String. The prototype. The charAt ()
  • Example:
var str = 'hello'
console.log(str.charAt(0))  // h
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  • Note: If not writtenindex, the defaultindex 为 0
  • And index operation[]In contrast, index access does not returnundefinedAnd thecharAtReturns an empty string. In other words,charAtAlways return a string.

indexOf()

  • Purpose: To get the index of the first occurrence of a given string in the current string, or return if not found- 1
  • Grammar:str.indexOf(searchValue [, fromIndex])
  • searchValueIs the string to be found.
  • Reference: String. Prototype. IndexOf ()
  • Example:
console.log('hello world'.indexOf('w'))  / / 6

'hello world'.indexOf(' ')  / / 0
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lastIndexOf()

  • Purpose: To find the index of the first occurrence of a given string in the current string from back to front, if not found, return- 1
  • Grammar:str.lastIndexOf(searchValue[, fromIndex])
  • Reference: String. The prototype. The lastIndexOf ()
  • Example:
var str = 'Brave new world'
console.log(str.lastIndexOf('new'))  / / 6
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includes()

  • Purpose: Determine whether the current string contains the given string
  • Grammar:str.includes(searchString[, position])
  • searchStringIs the string to be found
  • positionFor fromstrAt which index of, the search for substrings begins. The default is0.
  • Reference: String. Prototype. Includes ()
  • Example:
// includes is case sensitive
'Blue Whale'.includes('blue'); // returns false
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startsWith()

  • Purpose: Determine whether the current string has been given the beginning of the string
  • Grammar:str.startsWith(searchString[, position])
  • positionIs the initial search location
  • The reference String. Prototype. StartsWith ()
  • Example:
// startsWith is case-sensitive
var str = 'hello'
console.log(str.startsWith('Hell'))  // false
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endsWith()

  • Purpose: Determine whether the current string ends with the given string
  • Grammar:str.endsWith(searchString[, length])
  • length 为 strThe default value isstr.length
  • Reference: String. Prototype. EndsWith ()
  • Example:
var str = 'hello'
console.log(str.endsWith('llo'))  // true

// length specifies the length of the string, which is equivalent to the index without the string
var str = "To be, or not to be, that is the question.";

alert( str.endsWith("question."));// true
alert( str.endsWith("to be"));// false
alert( str.endsWith("to be".19));// true

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padStart()

  • Purpose: Padding the current string with the given string, starting from the left, so that the final length reaches the specified length, the excess will be truncated.
  • Grammar:str.padStart(targetLength [, padString])
  • padStringDefault is space' '
  • Reference: String. Prototype. PadStart ()
  • Example:
console.log('abc'.padStart(10.'nihao'))  // nihaoniabc
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padEnd()

  • Purpose: Padding the current string with the given string, starting from the right, so that the final length reaches the specified length, the excess will be truncated.
  • Grammar: ` `
  • Reference: String. Prototype. PadEnd ()
  • Example:
console.log('abc'.padEnd(8.The '*'))  // abc*****
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repeat()

  • Purpose: Repeat the current string a given number of times to return a new string.
  • Grammar:str.repeat(count)
  • If I don’t give youcount.countThe default is0
  • ifcount 为 0, returns an empty string
  • Reference: String. Prototype. Repeat ()
  • Example:
'abc'.repeat()  / /"
'abc'.repeat(0)  / /"
'abc'.repeat(2)  // 'abcabc'
// 3.7 is automatically truncated to 3
'abc'.repeat(3.7)  // 'abcabcabc'
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concat()

  • Purpose: Concatenate one or more strings and return a new string
  • Grammar:str.concat(str2, [, ...strN])
  • Performance:Highly recommended use+ 和 + =Instead ofconcatmethods.
  • Reference: String. The prototype. The concat ()
  • Example:
' '.concat(1.2.3)  / / '123'
'hello'.concat(' '.'world')  // 'hello world'
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replace()

  • Purpose: To replace the old string in the current string with a new string, replacing only the first match and returning a brand new string
  • Grammar:str.replace(regexp|substr, newSubStr|function)
  • Reference: String. The prototype. The replace ()
  • Example:
var str = 'apple'
var newStr = str.replace('apple'.'pear')
console.log(newStr)  // pear
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search()

  • Purpose: To find the index of the first occurrence of a given string in the current string
  • Grammar:str.search(regexp)
  • regexpIs a regular expression object that is used if a non-regular expression is passed innew RegExp(regexp)
  • Reference: String. The prototype. The search ()
  • Example:
console.log('hello'.search('el'))  / / 1
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split()

  • Purpose: Split the current string into arrays based on the separator and the number of cuts and return them
  • Grammar:str.split([separator[, limit]])
  • If no argument is passed, an array with the original string is returned. ifseperator 为 ' ', returns an array of single characters. This method is closely related toPython 中 str.split()Not quite the same,PythonDefaults to whitespace characters.
  • limitRepresents the maximum length of the returned array (PythonOf the string insplit()Method, the second parametermaxsplitRepresents the maximum number of cuts)
  • Reference: String. The prototype. The split ()
  • Example:
var str = 'hello world'
var arr = str.split('o')
console.log(arr)  // ['hell', 'w', 'rld']
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substr() 与 substring()

  • Purpose: To intercept a substring from the current string
  • Note:substr()Is a legacy function, use it whenever possiblesubstring()Instead of it
  • substr()Grammar:str.substr(start[, length])It’s kind of likeCThe language of thesubstr(pos, len)Function.
  • substring()Grammar:str.substring(indexStart[, indexEnd])Not at the time of interceptionindexEndThe character corresponding to the index
  • Reference: String. The prototype. The substr ()
  • Reference: String. The prototype. The substring ()
  • Example:
'hello'.substring(1.3)  // 'el'
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toLowerCase()

  • Purpose: To convert the current string to lowercase and return a new string
  • Grammar:str.toLowerCase()
  • Reference: String. Prototype. ToLowerCase ()
  • Example:
'Abc'.toLowerCase()  // abc
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toUpperCase()

  • Purpose: To convert the current string to uppercase and return a new string
  • Grammar:
  • Reference: String. The prototype. The toUpperCase ()
  • Example:
'Abc'.toUpperCase()  // ABC
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trim()

  • Purpose: Remove whitespace characters from both sides of the current string and return a new string
  • Grammar:str.trim()
  • Reference: String. The prototype. The trim ()
  • Example:
'\t\nfoo \n'.trim()
'foo'
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